Joint inversion

Surface-wave analysis can be performed according to a multitude of approaches. In fact, both the determination of the dispersive properties and data inversion can be accomplished according to several possible techniques, which should be chosen on a case-by-case basis, depending on the goals and site characteristics. The Miniature Array Analysis of Microtremors (MAAM) is an interesting methodology aimed at extracting the dispersive properties of the vertical (Z) component of Rayleigh waves from passive data recorded according to a circular-symmetry array. Compared to other techniques, MAAM can investigate larger wavelengths and provide phase velocities in a wider frequency range (a triangular array with a radius of a couple of meters can provide the dispersion curve in the 2-20 Hz frequency range, approximatively). Despite its remarkable potential, MAAM can be affected by industrial noise that alters the natural microtremor field. The comparative analysis of the Z-component dispersion retrieved via Extended Spatial AutoCorrelation (ESAC) and MAAM is initially conducted to validate the adopted procedures and verify the paradigms to adopt to identify the frequency range properly investigated. Following this, analysing a second time-lapse dataset, the effects of industrial components on both the dispersion curve obtained via MAAM and the Horizontal-to-Vertical Spectral Ratio (HVSR) are investigated. The experimental evidences show that non-monochromatic industrial components can have a malicious effect on both MAAM and HVSR. In this context, analysing the coherence functions of the multi-component data recorded by a 3-component geophone, together with the spectral ratio and noise-to-signal ratio obtained during MAAM processing, is crucial for assessing the possible presence of industrial components that may affect the observables ultimately used in the joint inversion.

The Mw 9.2 Sumatra earthquake of December 26, 2004, like other huge Earthquakes of the past, denotes the difficulty of the science to understand such extended seismic sources. In this work we intended to explain the project SISMOD that have as main purpose the deployment of a computational algorithm to perform the systematic and detailed study of extended seismic sources, independently its dimension and geometry. The method it will be structured to operate from a joint utilization of strong motions; teleseismic waveforms and geodetic data (GPS and InSAR)

The Global Positioning System (GPS) network in Japan detected coseismic deformation from the 2007 Noto Hanto earthquake (M w = 6.9). The result indicates a 21-cm southwestward displacement and a 7-cm upheaval at the GPS site near the epicenter. Synthetic Aperture Interferometry (InSAR) shows an approximately 50-cm movement toward the “Daichi” satellite, in ascending orbit, near the epicenter. The estimated fault slip distribution based on GPS and InSAR results shows a large slip area ranging up to 2 m near and northeast of the hypocenter. The slip area beneath the Sea of Japan southwest of the hypocenter also shows large slippage of around 2 m. Aftershocks are distributed in the asperity area and its vicinity, demonstrating that the asperity hypothesis clearly does not hold completely for this earthquake. Computed vertical displacements using the model are consistent with the geomorphological evidence of long-term uplift.

The Colorado Plateau is a physiographic province in the western US with an average elevation of $1.9 km where, in contrast to neighboring provinces, there is little evidence of large scale tectonic deformation or magmatism. Recent availability of Earthscope/ USArray seismic data allow us to better examine the crust and upper mantle structure beneath the region and test proposed explanations for the plateau's uplift and relative stability. Using phase velocities for fundamental mode Rayleigh waves and P receiver functions, we perform over 800 joint inversions for 1-D shear wave velocity V S profiles sampling the plateau and surrounding regions down to 150 km depth. We image a sharp change in crustal thickness at the western edge of the Colorado Plateau with a more gradual increase eastward moving into the Rocky Mountains. A relatively thick (≳100 km) lithosphere beneath the plateau extends into the Rocky Mountains to the north. We use empirical scaling relations to estimate densities from our V S results, and predict the associated gravity anomalies, which are inconsistent with the observed distribution of the Bouguer gravity anomalies. We somewhat reconcile the prediction and observations by assuming that lateral density variations below 50 km can be ignored and the lithospheric root is therefore neutrally buoyant. While there is some evidence for small scale convection and lithospheric removal at its edges, the shape of the lithospheric mantle anomaly is consistent with a large scale uplift of the plateau by heating since removal of the Farallon slab. We conclude that the lithospheric root is key to the long term stability of the Colorado Plateau, leading to a colder, stronger crust.

The thick crust of the southern Tibetan and central Andean plateaus includes high-conductivity, low-velocity zones ascribed to partial melt. The melt origin and effect on plateau uplift remain speculative, in particular if plateau uplift happens before continental collision. The East Anatolian Plateau (EAP) has experienced similar, more recent uplift but its structure is largely unknown. Here we present an 80 km deep geophysical model across EAP, constrained by seismic receiver functions integrated with interpretation of gravity data and seismic tomographic, magnetotelluric, geothermal, and geochemical models. The results indicate a 20 km thick lower crustal layer and a 10 km thick midcrustal layer, which both contain pockets of partial melt. We explain plateau uplift by isostatic equilibration following magmatism associated with roll-back and break-off of the Neo-Tethys slab. Our results suggest that crustal thickening by felsic melt and mafic underplate are important for plateau uplift in the EAP, Andes and Tibet.

In order to understand the subsurface stratigraphy and structure of the northwest end of the Turkana Basin, Northern Kenya Rift, we used 2-D joint inversion of magnetotelluric (MT) and gravity data acquired along 3 profiles perpendicular to the main Murua Rith-Lapur Rift Border Fault. The regional geology is characterized by a basement of Precambrian age overlain by a ≤500-m thick sandstone formation named the Lapur

Neste trabalho é apresentada uma metodologia baseada no cruzamento de técnicas e dados sísmicos (ondas de volume com registo telessísmico por estações de banda larga) e geodésicos (SAR-Radar de Abertura Sintética) com o intuito de estudar o complexo processo de ruptura do sismo do Haiti de 12 de Janeiro de 2010. Esta metodologia baseia-se: 1) na análise da diretividade para estimar a direção e a velocidade média de ruptura; b) inversão de ondas de volume para reconstituição do modelo cinemático de ruptura (distribuição espaço-temporal de deslizamentos); 3) modelação da deformação cossísmica, a partir dos resultados do modelo de fonte obtido por inversão de dados sísmicos, e comparação com a correspondente deformação medida com dados SAR, para aferição do modelo de fonte obtido. A aplicação desta metodologia ao sismo do Haiti revela uma ruptura complexa que se propaga de ENE para OSO sobre um plano de falha inclinado para norte, com uma velocidade média de 2.5km/s, durante aproximadamente 12s. A ruptura é composta basicamente por duas asperidades: a primeira (e mais significativa) ocorre durante os primeiros 5s de ruptura e ocupa uma área aproximadamente circular com cerca de 6km de raio, centrada no hipocentro; a segunda ocorre nos últimos 6s de ruptura, cobre uma superfície rectangular com cerca de 10km de comprimento (ao longo da direção da ruptura) por 3km de largura (na direção da inclinação). Os vetores deslizamento mostram que a primeira asperidade tem mecanismo compatível com desligamento esquerdo com uma pequena componente inversa e o mecanismo da segunda asperidade é semelhante ao mecanismo da primeira asperidade.

To define the procedures necessary to unambiguously define the subsurface model, a comprehensive set of active and passive seismic data was collected in an industrial area characterized by an extremely high level of background microtremors. Passive data are recorded to define three observables: the dispersion curve of the vertical component of Rayleigh waves via miniature array analysis of microtremors, the Love-wave dispersion curve via extended spatial autocorrelation, and the horizontal-to-vertical spectral ratio (HVSR). Active data used for the holistic analysis of surface waves are extracted from data recorded through a hybrid acquisition procedure accomplished with only two 3C geophones used to simultaneously define the HVSR at two points. Defined observables are combined according to three different approaches: the joint analysis of Rayleigh waves and HVSR, the joint analysis of Rayleigh and Love waves together with the HVSR, and the joint analysis of multicomponent group velocities together with the HVSR and Rayleigh-wave particle motion (RPM) curves. In agreement with the theory, data indicate that, in general, surface-wave modeling cannot be performed considering modal dispersion curves: dispersion obtained from passive data needs to be modeled considering the effective curve, whereas group velocity obtained from active data can be analyzed using the full velocity spectrum technique. Results indicate that joint inversion of Rayleigh-wave dispersion and HVSR does not necessarily ensure the correctness of the obtained S-wave velocity (𝑉s) profile and that Love waves represent a key observable to fully constrain an unambiguous inversion procedure. However, the joint analysis of multicomponent group velocity spectra (from active multicomponent single-offset data) together with the HVSR and RPM curves is a further efficient way to obtain robust 𝑉s profiles through the active and passive data obtained by a single 3C geophone.

SUMMARYOur limited knowledge of the relationship between changes in the state of an aquifer or reservoir and the corresponding changes in the elastic moduli, that is the rock physics model, hampers the effective use of time-lapse seismic observations for estimating flow properties within the Earth. A central problem is the complicated dependence of the magnitude of time-lapse changes on the saturation, pressure, and temperature changes within an aquifer or reservoir. We describe an inversion methodology for reservoir characterization that uses onset times, the calendar time of the change in seismic attributes, rather than the magnitude of the changes. We find that onset times are much less sensitive than magnitudes to the rock physics model used to relate time-lapse observations to changes in saturation, temperature and fluid pressure. We apply the inversion scheme to observations from daily monitoring of enhanced oil recovery at the Peace River field in Canada. An array of 1492 bur...

The Colorado Plateau is a physiographic province in the western US with an average elevation of $1.9 km where, in contrast to neighboring provinces, there is little evidence of large scale tectonic deformation or magmatism. Recent availability of Earthscope/ USArray seismic data allow us to better examine the crust and upper mantle structure beneath the region and test proposed explanations for the plateau's uplift and relative stability. Using phase velocities for fundamental mode Rayleigh waves and P receiver functions, we perform over 800 joint inversions for 1-D shear wave velocity V S profiles sampling the plateau and surrounding regions down to 150 km depth. We image a sharp change in crustal thickness at the western edge of the Colorado Plateau with a more gradual increase eastward moving into the Rocky Mountains. A relatively thick (≳100 km) lithosphere beneath the plateau extends into the Rocky Mountains to the north. We use empirical scaling relations to estimate densities from our V S results, and predict the associated gravity anomalies, which are inconsistent with the observed distribution of the Bouguer gravity anomalies. We somewhat reconcile the prediction and observations by assuming that lateral density variations below 50 km can be ignored and the lithospheric root is therefore neutrally buoyant. While there is some evidence for small scale convection and lithospheric removal at its edges, the shape of the lithospheric mantle anomaly is consistent with a large scale uplift of the plateau by heating since removal of the Farallon slab. We conclude that the lithospheric root is key to the long term stability of the Colorado Plateau, leading to a colder, stronger crust.

Geometrical properties of an earthquake population can be described by summation of seismic potency tensors that provide a strain-based description of earthquake focal mechanisms. We apply this method to ∼170 000 potency tensors for 0 < M L ≤ 5 southern California earthquakes recorded between January 1984 and June 2003. We compare summed tensors for populations defined by faulting region and earthquake magnitude to investigate the relation between earthquake characteristics, tectonic domains and fault-related length scales. We investigate spatial scales ranging from ∼1-700 km and use the results to identify systematic differences between seismic behaviour for different faults and different regions. Our results show features that are indicative of both scale-invariant and scale-dependent processes. On the largest scale the overall potency tensor summation for southern California 0 < M L ≤ 5 earthquakes over ∼20 yr corresponds closely to a double-couple (DC) mechanism with slip direction parallel to relative plate motion. The summed tensors and derived quantities for the different regions show clear persistent variations that are related to the dominant tectonic regime of each region. Significant differences between the non-DC components of the summed tensors, which we relate to fault heterogeneity, indicate systematic differences in deformation associated with earthquake populations from different fault zones or different magnitude ranges. We find an increase of heterogeneity for populations of smaller earthquakes and for regions where faulting deviates strongly from the overall sense of deformation, even when corrected for quality. The results imply an overall organization of earthquake characteristics into domains that are controlled to first order by geometrical properties of the largest faults and the plate motion. Smaller scale characteristics are related to local variations in the orientation, complexity and size of faults.

The 12 November 1996 M w 7.7 Peru subduction zone earthquake occurred off the coast of southern Peru, near the intersection of the South American trench and the highest topographical point of the subducting Nazca Ridge. We model the broadband teleseismic P-waveforms from stations in the Global Seismic Network to constrain the source characteristics of this subduction zone earthquake. We have analyzed the vertical component P-waves for this earthquake to constrain the depth, source complexity, seismic moment and rupture characteristics. The seismic moment determined from the nondiffracted P-waves is 3-5 ×10 20 N•m, corresponding to a moment magnitude M w of 7.6-7.7. The source time function for the 1996 Peru event has three pulses of seismic moment release with a total duration of approximately 45-50 seconds. The largest moment release occurs at approximately 35-40 seconds and is located 90 km southeast of the rupture initiation. Approximately 70% of the seismic moment was released in the third pulse. We find that the 1996 event reruptured part of the rupture area of the previous event in 1942. The location of the 1996 earthquake corresponds to a region along the Peru coast with the highest uplift rates of marine terraces. This suggests that the uplift may be due to repeated earthquakes such as the 1996 and 1942 events.

Until recently, little was known about the Weddell Sea sector of the West Antarctic Ice Sheet. In the last 10 years, a variety of expeditions and numerical modelling experiments have improved knowledge of its glaciology, glacial geology and tectonic setting. Two of the sector&#39;s largest ice streams rest on a steep reverse‐sloping bed yet, despite being vulnerable to change, satellite observations show contemporary stability. There is clear evidence for major ice sheet reconfiguration in the last few thousand years, however. Knowing precisely how and when the ice sheet has changed in the past would allow us to better understand whether it is now at risk. Two competing hypotheses have been established for this glacial history. In one, the ice sheet retreated and thinned progressively from its Last Glacial Maximum position. Retreat stopped at, or very near, the present position in the Late Holocene. Alternatively, in the Late Holocene, the ice sheet retreated significantly upstream ...

We present a joint analysis of newly acquired gravity and teleseismic data in the North Tanzanian Divergence, where the lithospheric break-up is at its earliest stage. The impact of a mantle upwelling in more mature branches of the East African Rift has been extensively studied at a lithospheric scale. However, few studies have been completed that relate the deep-seated mantle anomaly detected in broad regional seismic tomography with the surface deformation observed in the thick Archaean Pan-African suture zone located in North Tanzania. Our joint inversion closes the gap between local and regional geophysical studies, providing velocity and density structures from the surface down to ca. 250 km depth with new details. Our results support the idea of a broad mantle upwelling rising up to the lithosphere and creating a thermal modification along its path. However, our study clearly presents an increasing amplitude of the associated anomaly both in velocity and density above 200 km depth, which cannot be solely explained by a temperature rise. We infer from our images the combined impact of melt (2-3 per cent), composition and hydration that accompany the modification of a thick heterogenous cratonic lithosphere are a response to the hot mantle rising. The detailed images we obtained in density and velocity assert that Archaean and Proterozoic units interact with the mantle upwelling to restrict the lithosphere modifications within the Magadi-Natron-Manyara rift arm. The composition and hydration variations associated with those units equilibrate the thermal erosion of the craton root and allow for its stability between 100 and 200 km depth. Above 80 km depth, the crustal part is strongly affected by intruding bodies (melt and gas) which produces large negative anomalies in both velocity and density beneath the main magmatic centres. In addition to the global impact of a superplume, the velocity and density anomaly pattern suggests a 3-D distribution of the crust and mantle lithospheric stretching, which is likely to be controlled by inherited fabrics and enhanced by lateral compositional and hydration variations at the Tanzanian craton-orogenic belt boundary.

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The Central Andes is a key global location to study the enigmatic relation between volcanism and plutonism because it has been the site of large ignim briteforming eruptions during the past several million years and currently hosts the world's largest zone of silicic partial melt in the form of the Alti plano Puna Magma (or Mush) Body (APMB) and the Southern Puna Magma Body (SPMB). In this themed issue, results from the recently completed PLUTONS project are synthesized. This project focused an interdisciplinary study on two regions of largescale surface uplift that have been found to represent ongoing movement of magmatic fluids in the middle to upper crust. The loca tions are Uturuncu in Bolivia near the center of the APMB and Lazufre on the Chile Argentina border, on the edge of the SPMB. These studies use a suite of geological, geochemical, geophysical (seismology, gravity, surface defor ma tion, and electromagnetic methods), petrological, and geomorphological techniques with numerical modeling to infer the subsurface distribution, quantity, and movements of magmatic fluids, as well as the past history of eruptions. Both Uturuncu and Lazufre show separate geophysical anomalies in the upper, middle, and lower crust (e.g., low seismic velocity, low resistiv ity, etc.) indicating multiple distinct reservoirs of magma and/or hydrothermal fluids with different physical properties. The characteristics of the geophysical anomalies differ somewhat depending on the technique used-reflecting the different sensitivity of each method to subsurface melt (or fluid) of different compositions, connectivity, and volatile content and highlight the need for integrated, multidisciplinary studies. While the PLUTONS project has led to significant progress, many unresolved issues remain and new questions have been raised.

We use seismic and geodetic data both jointly and separately to constrain coseismic slip from the 12 November 1996 Mw 7.7 and 23 June 2001 Mw 8.5 southern Peru subduction zone earthquakes, as well as two large aftershocks following the 2001 earthquake on 26 June and 7 July 2001. We use all available data in our inversions: GPS, interferometric synthetic aperture radar (InSAR) from the ERS‐1, ERS‐2, JERS, and RADARSAT‐1 satellites, and seismic data from teleseismic and strong motion stations. Our two‐dimensional slip models derived from only teleseismic body waves from South American subduction zone earthquakes with Mw &gt; 7.5 do not reliably predict available geodetic data. In particular, we find significant differences in the distribution of slip for the 2001 earthquake from models that use only seismic (teleseismic and two strong motion stations) or geodetic (InSAR and GPS) data. The differences might be related to postseismic deformation or, more likely, the different sensitivit...

of southern Peru, near the intersection of the South American trench and the highest topographical point of the subducting Nazca Ridge. We model the broadband teleseismic P-waveforms from stations in the Global Seismic Network to constrain the source characteristics of this subduction zone earth-quake. We have analyzed the vertical component P-waves for this earthquake to constrain the depth, source complexity, seismic moment and rupture characteristics. The seismic moment determined from the nondiffracted P-waves is 3–5×1020 N·m, corresponding to a moment magnitude Mw of 7.6–7.7. The source time function for the 1996 Peru event has three pulses of seismic moment release with a total duration of approximately 45–50 seconds. The largest moment release occurs at approximately 35–40 seconds and is located 90 km southeast of the rupture initiation. Approximately 70 % of the seismic moment was released in the third pulse. We find that the 1996 event reruptured part of the rupture area of...

The Central Andes is a key global location to study the enigmatic relation between volcanism and plutonism because it has been the site of large ignim briteforming eruptions during the past several million years and currently hosts the world's largest zone of silicic partial melt in the form of the Alti plano Puna Magma (or Mush) Body (APMB) and the Southern Puna Magma Body (SPMB). In this themed issue, results from the recently completed PLUTONS project are synthesized. This project focused an interdisciplinary study on two regions of largescale surface uplift that have been found to represent ongoing movement of magmatic fluids in the middle to upper crust. The loca tions are Uturuncu in Bolivia near the center of the APMB and Lazufre on the Chile Argentina border, on the edge of the SPMB. These studies use a suite of geological, geochemical, geophysical (seismology, gravity, surface defor ma tion, and electromagnetic methods), petrological, and geomorphological techniques with numerical modeling to infer the subsurface distribution, quantity, and movements of magmatic fluids, as well as the past history of eruptions. Both Uturuncu and Lazufre show separate geophysical anomalies in the upper, middle, and lower crust (e.g., low seismic velocity, low resistiv ity, etc.) indicating multiple distinct reservoirs of magma and/or hydrothermal fluids with different physical properties. The characteristics of the geophysical anomalies differ somewhat depending on the technique used-reflecting the different sensitivity of each method to subsurface melt (or fluid) of different compositions, connectivity, and volatile content and highlight the need for integrated, multidisciplinary studies. While the PLUTONS project has led to significant progress, many unresolved issues remain and new questions have been raised.

When a nil zone is present in the subsurface salt structure, it effectively creates an annihilator of density contrast that gives rise to zero gravity response on the surface. As a result, part of the salt structure is invisible to the surface data and inversion algorithms often have difficulties in recovering the salt structure correctly. We develop a binary inversion technique in which the density contrast is restricted to being one of the two possibilities: either zero or the value expected at a given depth. The binary condition places a strong restriction on the admissible models so that the non-uniqueness caused by nil zones can be resolved. In this presentation, we will outline the formulation, discuss the solution strategy, and illustrate it with numerical examples.

The Nechalacho deposit is a world-class rare earth element deposit located in the Thor Lake region approximately 100 kilometers southwest of Yellowknife, NT, Canada. Located within the Blatchford Lake Intrusion Complex, this deposit has the potential to be a large-scale economic asset due to its relatively shallow and sub-horizontal geometry. In this study, geophysical inversion techniques are used to model subsurface magnetic susceptibility and density in order to delineate the deposit. Isolated and joint inversion of both magnetic and gravity data provide similar models. Each inversion procedure delineates a shallow, subhorizontal layer of high susceptibility and density in approximately the same location. This layer is interpreted to be the Nechalacho deposit and it extends further north than previously determined. Finally, magnetic susceptibilities were measured on selected samples using laboratory instruments to check the quality of previous field measurements as well as to validate and derive relationships between geophysical and mineralogical properties in the deposit.

We present two case studies of the application of seismic surveys to estimate the elastic properties of soil and rock in the shallow subsurface. The two sites present very different geological characteristics. The first test site is a town on the Croatian coast, not far from the city of Split, built on hard rock, where we acquired three seismic lines. The second site is located in the outskirts of the city of Ferrara, in Italy, in an alluvial plain, where two lines were acquired. In both sites, for detailed characterization, we acquired surface-, compressional- and shear-waves, further distinguishing the latter between horizontally (SH) and vertically (SV) polarized wavefields. We processed the data by performing a Multichannel Analysis of Surface Waves to compute a preliminary one-dimensional shear wave velocity profile. Then, we performed first-break tomography to compute P-, SH- and SV-velocity profiles. Such unusual acquisition allowed us to compute not only basic engineering pa...

For the seismic and dynamic design of the civil eng ineering projects a significant role is assumed by the geotechnical-seismic characterization of the site. The new Italian seismic code as well as the Eurocod es and other international seismic codes require the seismic sit e classification made on the basis of the shear wav e velocity profile. Among the several techniques of site inves tigation the MASW method (Multichannel Analysis of Surface Waves) and the ReMi method (Refraction Microtremors ) allow the determination of the shear wave velocit y profile and hence the seismic site classification by means of the measurement and the consequent analysis of t he Rayleigh waves. The article proposes a joint application of b th the active MASW and the ReMi to a real case in order to compare the two complementary methods.

Surface wave tests are non-invasive seismic techniques that have traditionally been used to determine the shear wave velocity (i.e. shear modulus) profile of soil deposits and pavement systems. Recently, Rix et al. [J. Geotech. Geoenviron. Engng 126 (2000) 472] developed a procedure to obtain near-surface values of material damping ratio from measurements of the spatial attenuation of Rayleigh waves. To date, however, the shear wave velocity and shear damping ratio profiles have been determined separately. This practice neglects the coupling between surface wave phase velocity and attenuation that arises from material dispersion in dissipative media. This paper presents a procedure to measure and invert surface wave dispersion and attenuation data simultaneously and, thus, account for the close coupling between the two quantities. The methodology also introduces consistency between phase velocity and attenuation measurements by using the same experimental configuration for both. The new approach has been applied at a site in Memphis, TN and the results obtained are compared with independent measurements.

High resolution structures of the lithosphere-asthenosphere system beneath a seismic profile in Iran are obtained by the simultaneous inversion of data from receiver functions and fundamental mode Rayleigh wave group velocity and validated by modeling Bouguer gravity anomaly data. The seismic data are gathered over a profile extending across Zagros, Sanandaj-Sirjan Zone (SSZ), Urumieh-Dokhtar magmatic arc (UDMA), Central Iran, Alborz-Binalud Mountain ranges and Kopeh Dagh Mountain ranges. The results confirm the presence of crustal roots at the north and south of Iranian Plateau where it meets the Arabian Plate and Eurasia. The high velocity lithosphere of the Arabian Plate gently plunges NNE-ward beneath Central Iran supporting the subduction of the continental lithosphere responsible for the seismicity of the area. The crust and lithosphere are thinner beneath Central Iran, where two low velocity structures are very likely related to magma sources of the UDMA and in east of Iran, around Lut block, where the volcanism shows calcalkaline subduction-related geochemistry. The crustal-lithospheric root to the north of the Iranian Plateau may represent the relict of a previous "cimmeric" subduction zone. Therefore the Iranian lithosphere-asthenosphere system could be the result of the coalescence of two separate subduction zones.

of southern Peru, near the intersection of the South American trench and the highest topographical point of the subducting Nazca Ridge. We model the broadband teleseismic P-waveforms from stations in the Global Seismic Network to constrain the source characteristics of this subduction zone earth-quake. We have analyzed the vertical component P-waves for this earthquake to constrain the depth, source complexity, seismic moment and rupture characteristics. The seismic moment determined from the nondiffracted P-waves is 3–5×1020 N·m, corresponding to a moment magnitude Mw of 7.6–7.7. The source time function for the 1996 Peru event has three pulses of seismic moment release with a total duration of approximately 45–50 seconds. The largest moment release occurs at approximately 35–40 seconds and is located 90 km southeast of the rupture initiation. Approximately 70 % of the seismic moment was released in the third pulse. We find that the 1996 event reruptured part of the rupture area of...

SUMMARYOur limited knowledge of the relationship between changes in the state of an aquifer or reservoir and the corresponding changes in the elastic moduli, that is the rock physics model, hampers the effective use of time-lapse seismic observations for estimating flow properties within the Earth. A central problem is the complicated dependence of the magnitude of time-lapse changes on the saturation, pressure, and temperature changes within an aquifer or reservoir. We describe an inversion methodology for reservoir characterization that uses onset times, the calendar time of the change in seismic attributes, rather than the magnitude of the changes. We find that onset times are much less sensitive than magnitudes to the rock physics model used to relate time-lapse observations to changes in saturation, temperature and fluid pressure. We apply the inversion scheme to observations from daily monitoring of enhanced oil recovery at the Peace River field in Canada. An array of 1492 bur...

In oscillatory shear experiments, the values of the storage and loss moduli, G (ω) and G (ω), respectively, are only measured and recorded for a number of values of the frequency ω in some well-defined finite range [ω min , ω max ]. In many practical situations, when the range [ω min , ω max ] is sufficiently large, information about the associated polymer dynamics can be assessed by simply comparing the interrelationship between the frequency dependence of G (ω) and G (ω). For other situations, the required rheological insight can only be obtained once explicit knowledge about the structure of the relaxation time spectrum H(τ) has been determined through the inversion of the measured storage and loss moduli G (ω) and G (ω). For the recovery of an approximation to H(τ), in order to cope with the limited range [ω min , ω max ] of the measurements, some form of localization algorithm is required. A popular strategy for achieving this is to assume that H(τ) has a separated discrete point mass (Dirac delta function) structure. However, this expedient overlooks the potential information contained in the structure of a possibly continuous H(τ). In this paper, simple localization algorithms and, in particular, a joint inversion least squares procedure, are proposed for the rapid recovery of accurate approximations to continuous H(τ) from limited measurements of G (ω) and G (ω).

The Lazufre Volcanic System (LVS), on the border of northern Chile and Argentina, is an active complex of two volcanoes, Lastarria to the north and Cordón del Azufre to the south. The LVS is not regularly monitored with any scientific equipment despite being recognized as a top ten volcanic hazard in Argentina by the Observatorio Argentino de Vigilancia Volcánica of the Servicio Geológico y Minero Argentino. The system has shown unusual inflation signatures observed in InSAR but the level of seismic activity and its spatial and temporal distribution were unknown due to the lack of a permanent local seismic network. The PLUTONS Project deployed eight broadband seismic stations throughout the LVS between November 2011 and March 2013. This study shows event locations and types from November 2011 through March 2012. We analyze 591 seismic events within 20 km of Lastarria. Most events cluster tightly beneath Lastarria and almost no activity is observed beneath Cordón del Azufre or the primary inflation center. All events are reviewed manually, and located using a velocity model that assimilates prior studies and accounts for hypocenters within the edifice up to 5 km above sea level. More than 90% of the resulting hypocenters are shallower than 10 km below sea level. The waveforms have characteristics similar to those observed at many other volcanoes, suggesting five classes of events: volcano-tectonic (VT), longperiod 1 (LP1), long period 2 (LP2), hybrid (HY), and unknown (X). Frequencymagnitude analysis reveals distinct b-values ranging from 1.2 for VT events to 2.5 for LP1 events. Based on the spatial distribution of events and the b-values, we infer that seismic activity is driven mainly by movement of fluids and gases associated with the regional magma zones and inflation centers. The seismic activity is energetic at times, and quieter at others, suggesting the presence of episodic magmatic and/or hydrothermal activity, focused at Lastarria. Our findings indicate that the previously observed inflation signals are indeed volcanic in origin. These results also demonstrate the potential for success of a future seismic monitoring system and provide a framework for interpreting the subsequent observations, both of which are critical to assessing the volcanic risk of the northern Chile-Argentina region.

We use Interferometric Synthetic Aperture Radar (InSAR), teleseismic body waves, tsunami waveforms recorded by tsunameters, field observations of coastal uplift, subsidence and run-up to develop and test a refined model of the spatio-temporal history of slip during the Mw 8.0 Pisco earthquake of August 15 th , 2007. Our preferred solution shows two distinct patches of high slip. One patch is located near the epicenter while another larger patch ruptured 60 km further south, at the latitude of the Paracas peninsula. Slip on the second patch started 60 sec after slip initiated on the first patch. We observed a remarkable anti-correlation between the co-seismic slip distribution and the aftershock distribution determined from the Peruvian seismic network. The proposed source model is compatible with regional run-up measurements and open-ocean tsunami records. From the latter dataset, we identified the 12 min timing error of the tsunami forecast system as being due to a mislocation of the source, caused by the use of only one tsunameter located in a non-optimal azimuth. The comparison of our source model with the tsunami observations validate that the rupture did not extend to the trench, and confirms that the Pisco event is not a tsunami earthquake despite its low apparent rupture velocity (< 1.5 km/s). We favor the interpretation that the earthquake consists of 2 subevents, each with a conventional rupture velocity (2-4 km/s). The delay between the 2 subevents might reflect the time for the second shock to nucleate or, alternatively, the time it took for afterslip to increase the stress level on the second asperity to a level necessary for static triggering. The source model predicts uplift offshore and subsidence onland with the pivot line following closely the coastline. This pattern is consistent with our observation of very small vertical displacement along the shoreline when we visited the epicentral area in the days following the event. This earthquake represents, to our knowledge, one of the best examples of a link between the geomorphology of the coastline and the pattern of surface deformation induced by large interplate ruptures.

The Lazufre Volcanic System (LVS), on the border of northern Chile and Argentina, is an active complex of two volcanoes, Lastarria to the north and Cordón del Azufre to the south. The LVS is not regularly monitored with any scientific equipment despite being recognized as a top ten volcanic hazard in Argentina by the Observatorio Argentino de Vigilancia Volcánica of the Servicio Geológico y Minero Argentino. The system has shown unusual inflation signatures observed in InSAR but the level of seismic activity and its spatial and temporal distribution were unknown due to the lack of a permanent local seismic network. The PLUTONS Project deployed eight broadband seismic stations throughout the LVS between November 2011 and March 2013. This study shows event locations and types from November 2011 through March 2012. We analyze 591 seismic events within 20 km of Lastarria. Most events cluster tightly beneath Lastarria and almost no activity is observed beneath Cordón del Azufre or the primary inflation center. All events are reviewed manually, and located using a velocity model that assimilates prior studies and accounts for hypocenters within the edifice up to 5 km above sea level. More than 90% of the resulting hypocenters are shallower than 10 km below sea level. The waveforms have characteristics similar to those observed at many other volcanoes, suggesting five classes of events: volcano-tectonic (VT), longperiod 1 (LP1), long period 2 (LP2), hybrid (HY), and unknown (X). Frequencymagnitude analysis reveals distinct b-values ranging from 1.2 for VT events to 2.5 for LP1 events. Based on the spatial distribution of events and the b-values, we infer that seismic activity is driven mainly by movement of fluids and gases associated with the regional magma zones and inflation centers. The seismic activity is energetic at times, and quieter at others, suggesting the presence of episodic magmatic and/or hydrothermal activity, focused at Lastarria. Our findings indicate that the previously observed inflation signals are indeed volcanic in origin. These results also demonstrate the potential for success of a future seismic monitoring system and provide a framework for interpreting the subsequent observations, both of which are critical to assessing the volcanic risk of the northern Chile-Argentina region.

A method for history matching of an in-house petroleum reservoir compositional simulator with multipoint flux approximation is presented. This method is used for the estimation of unknown reservoir parameters, such as permeability and porosity, based on production data and inverted seismic data. The limitedmemory Broyden-Fletcher-Goldfarb-Shanno method is employed for minimization of the objective function, which represents the difference between simulated and observed data. In this work, we present the key features of the algorithm for calculations of the gradients of the objective function based on adjoint variables. The test example shows that the method is applicable to cases with anisotropic permeability fields, multipoint flux approximation, and arbitrary fluid compositions.

The Altiplano-Puna magma body (APMB) is recognized as one of the largest crustal magma bodies on Earth. Geophysical studies have detected a thin low velocity zone at a depth of about 20 km that is inferred to be a layer of > 20% partial melt. Volcan Uturuncu, near the centre of the APMB, has been inflating over the past two decades at rates of 1-2 cm/year. Broadband magnetotelluric data collected at Volcan Uturuncu detected a region of low resistivity at a depth of about 20 km, believed to be the APMB. The magnetotelluric data have also shown pathways of fluid extending from the APMB to the surface, and suggest that the uplift is associated with magma movement towards the surface.

New volcanic unrest has been detected in the Domuyo Volcanic Center (DVC), to the east of the Andes Southern Volcanic Zone in Argentina. To better understand this activity, we investigated new seismic monitoring data, gravimetric and magnetic campaign data, and interferometric synthetic aperture radar (InSAR) deformation maps, and we derived an image of the magma plumbing system and the likely source of the unrest episode. Seismic events recorded during 2017–2018 nucleate beneath the southwestern flank of the DVC. Ground deformation maps derived from InSAR processing of Sentinel-1 data exhibit an inflation area exceeding 300 km2, from 2014 to at least March 2018, which can be explained by an inflating sill model located 7 km deep. The Bouguer anomaly reveals a negative density contrast of ~35 km wavelength, which is spatially coincident with the InSAR pattern. Our 3D density modeling suggests a body approximately 4–6 km deep with a density contrast of –550 kg/m3. Therefore, the geop...

of southern Peru, near the intersection of the South American trench and the highest topographical point of the subducting Nazca Ridge. We model the broadband teleseismic P-waveforms from stations in the Global Seismic Network to constrain the source characteristics of this subduction zone earth-quake. We have analyzed the vertical component P-waves for this earthquake to constrain the depth, source complexity, seismic moment and rupture characteristics. The seismic moment determined from the nondiffracted P-waves is 3–5×1020 N·m, corresponding to a moment magnitude Mw of 7.6–7.7. The source time function for the 1996 Peru event has three pulses of seismic moment release with a total duration of approximately 45–50 seconds. The largest moment release occurs at approximately 35–40 seconds and is located 90 km southeast of the rupture initiation. Approximately 70 % of the seismic moment was released in the third pulse. We find that the 1996 event reruptured part of the rupture area of...

The great Rat Islands underthrusting earthquake (Mw = 8.7), of February 4, 1965, represents subduction of the Pacific plate beneath the North American plate along a 600-km segment of the western end of the Aleutian Islands. Body wave inversion techniques are used to determine the spatial and temporal heterogeneities associated with the Rat Islands earthquake. We have deconvolved WorldWide Standard Seismograph Network long-period teleseismic P wave seismograms to obtain source time functions. Directivity associated with the three major pulses of moment release in the source time functions indicates a total source duration of 160 s, unilateral rupture in the direction 300 ø, fault length of 420 km, and average rupture velocity of 2.5 km/s. The three pulses of moment release are located along the fault, and these regions of high moment release are interpreted as asperities. The first asperity extends from the epicenter to 100 km to the WNW. This is the largest asperity and corresponds to a smooth pulse of moment release in the source time function with a duration of 50 s. The second pulse of moment release is very jagged, is less coherent between stations, and is centered-200 km WNW of the epicenter. The third pulse of moment release extends from 360 to 420 km WNW of the epicenter. Although the aftershock area is-600 km in length, we can not resolve any moment release from the P waves beyond-420 km WNW of the epicenter. The Rat Islands event was closely followed by a large tensional outer-rise event on March 30, 1965, (Ms-7.5), which is located oceanward of the largest moment release associated with the Rat Islands mainshock rupture. Detailed analysis of the P waves for this large outer-rise event confine the depth extent to the upper 30-35 km of the crust. The spatial and temporal association between the February 4 mainshock and the March 30 tensional outer-rise event suggests the tensional event may have been triggered by the large displacement near the mainshock epicenter. The overriding plate along the western Aleutian subduction zone is laterally segmented into a series of rigid tectonic blocks separated by fault controlled canyons and extensional basins (Geist et al., 1988). We suggest that the central undeformed parts of the blocks have the strongest coupling with the down-going plate and hence are the sites of the largest moment release during an underthrusting earthquake. The three asperities determined from the P waves correspond to the Rat, Buldir, and Near tectonic blocks respectively. Hence the P wave seismic moment release of the Rat Islands earthquake is controlled by the lateral segmentation of the overriding plate.

In recent years, the use of radiographic inspection with cosmic-ray muons has spread into multiple research and industrial fields. This technique is based on the highpenetration power of cosmogenic muons. Specifically, it allows the resolution of internal density structures of largescale geological objects through precise measurements of the muon absorption rate. So far, in many previous works, this muon absorption rate has been considered to depend solely on the density of traversed material (under the assumption of a standard rock) but the variation in chemical composition has not been taken seriously into account. However, from our experience with muon tomography in Alpine environments, we find that this assumption causes a substantial bias in the muon flux calculation, particularly where the target consists of high {Z 2 /A} rocks (like basalts and limestones) and where the material thickness exceeds 300 m. In this paper, we derive an energy loss equation for different minerals and we additionally derive a related equation for mineral assemblages that can be used for any rock type on which mineralogical data are available. Thus, for muon tomography experiments in which high {Z 2 /A} rock thicknesses can be expected, it is advisable to plan an accompanying geological field campaign to determine a realistic rock model.

Investigations made to evaluate the site-effect characteristics and to develop a reliable site classification scheme have received paramount importance for the urban areas planning and reliable sitespecific seismic hazard assessment. This paper presents a novel non-objective and data-driven approach for preliminary seismic site-specific classification maps using machine learning (ML) based on affinity propagation (AP) along with a selected set of representative horizontal to vertical spectral ratio (HVSR) curves inside King Saud University (KSU) campus, which is among the main areas in Saudi Arabia. Besides, the proposed model aims to overcome the clustering error due to the dependency of the interpreter's experience. Measurements of the ambient vibrations were performed to cover the entire campus area by about 307 stations. Recording at each station lasted for 20 minute length and a sample rate of 128 Hz for each station to satisfy the criteria for reliable and unambiguous HVSR results. Frequency and amplification values were used for subsequent site classification by passing messages between data points. The obtained results illustrate that the microtremor spectral ratio can be a remarkably robust tool in determining site effects. Accordingly, the proposed methodology can assist the decision-makers to set the priorities of managing land uses, estimating the earthquake losses, conducting programs for reducing the vulnerability of existing structures, enforcing building codes, planning for emergency response and long-term recovery, and designing and implementing phases of new constructions.

Rayleigh wave or ground roll is a noise in seismic body waves. However, how to use this noise for soil characterization is very interesting since Rayleigh wave phase velocity is a function of compression-wave velocity, shearwave velocity, density and layer thickness. In layered-medium Rayleigh wave velocity also depends on wavelength or frequency, and this phenomenon is called dispersion. Inversion procedure to get shear-wave velocity profile needs a priori information about the solution of the problem to limit the unknown parameters. The Lagrange multiplier method was used to solve the constrained optimization problems or well known as a smoothing parameter in inversion problems. The advantage of our inversion procedure is that it can guarantee the convergence of solution even though the field data is incomplete, insufficient, and inconsistent. The addition of smoothing parameter can reduce the time to converge. Beside numerical stability, the statistical stability is also involved in inversion procedure. In field experiment we extracted ground roll data from seismic refraction record. The dispersion curves had been constructed by applying f-k analysis and f-k dip filtering. The dispersion curves show the dependence of Rayleigh wave phase velocities in layered media to frequency. The synthetic models also demonstrate the stability and the speed of inversion procedure.

Tsunamis from the 2004 off the Kii Peninsula earthquakes (M 7.1 and 7.4) were recorded on offshore tsunami gauges, a GPS tsunami gauge and eight bottom-pressure gauges, as well as coastal tide gauges located south of Honshu and Shikoku. The maximum amplitudes on the GPS and bottom-pressure gauges were several to ten cm, while those on tide gauges were up to 0.9 m. We first computed tsunami waveforms from the earthquake source models proposed Yamanaka (2004) and Yagi (2004) from seismic waveform analysis, and compared them with the observed waveforms. For the first event (foreshock), both models produce similar waveforms with the observations. For the second event (mainshock), the waveforms computed from the Yamanaka model is closer to the observed waveforms, but there are still discrepancies between the observed and computed waveforms. We then performed tsunami waveform inversions to estimate the water height distributions in the source area. The foreshock source is ∼1600 km2 with t...

Tsunami earthquakes are a group of enigmatic earthquakes generating disproportionally large tsunamis relative to seismic magnitude. These events occur most typically near deep-sea trenches. Tsunami earthquakes occurring approximately every 10 years near Torishima on the Izu-Bonin arc are another example. Seismic and tsunami waves from the 2015 event [ (moment magnitude) = 5.7] were recorded by an offshore seafloor array of 10 pressure gauges, ~100 km away from the epicenter. We made an array analysis of dispersive tsunamis to locate the tsunami source within the submarine Smith Caldera. The tsunami simulation from a large caldera-floor uplift of ~1.5 m with a small peripheral depression yielded waveforms remarkably similar to the observations. The estimated central uplift, 1.5 m, is ~20 times larger than that inferred from the seismologically determined non-double-couple source. Thus, the tsunami observation is not compatible with the published seismic source model taken at face val...

Tsunamis from the 2004 off the Kii Peninsula earthquakes (M 7.1 and 7.4) were recorded on offshore tsunami gauges, a GPS tsunami gauge and eight bottom-pressure gauges, as well as coastal tide gauges located south of Honshu and Shikoku. The maximum amplitudes on the GPS and bottom-pressure gauges were several to ten cm, while those on tide gauges were up to 0.9 m. We first computed tsunami waveforms from the earthquake source models proposed Yamanaka (2004) and Yagi (2004) from seismic waveform analysis, and compared them with the observed waveforms. For the first event (foreshock), both models produce similar waveforms with the observations. For the second event (mainshock), the waveforms computed from the Yamanaka model is closer to the observed waveforms, but there are still discrepancies between the observed and computed waveforms. We then performed tsunami waveform inversions to estimate the water height distributions in the source area. The foreshock source is ≈1600 km2 with t...

We use seismic and geodetic data both jointly and separately to constrain coseismic slip from the 12 November 1996 M w 7.7 and 23 June 2001 M w 8.5 southern Peru subduction zone earthquakes, as well as two large aftershocks following the 2001 earthquake on 26 June and 7 July 2001. We use all available data in our inversions: GPS, interferometric synthetic aperture radar (InSAR) from the ERS-1, ERS-2, JERS, and RADARSAT-1 satellites, and seismic data from teleseismic and strong motion stations. Our two-dimensional slip models derived from only teleseismic body waves from South American subduction zone earthquakes with M w > 7.5 do not reliably predict available geodetic data. In particular, we find significant differences in the distribution of slip for the 2001 earthquake from models that use only seismic (teleseismic and two strong motion stations) or geodetic (InSAR and GPS) data. The differences might be related to postseismic deformation or, more likely, the different sensitivities of the teleseismic and geodetic data to coseismic rupture properties. The earthquakes studied here follow the pattern of earthquake directivity along the coast of western South America, north of 5°S, earthquakes rupture to the north; south of about 12°S, directivity is southerly; and in between, earthquakes are bilateral. The predicted deformation at the Arequipa GPS station from the seismic-only slip model for the 7 July 2001 aftershock is not consistent with significant preseismic motion.