How seismic anisotropy changes with scale

2020

Seismic reflection data (normal incidence and wide angle) are unique assets for solid Earth sciences as they provide critical information about the physical properties and structure of the lithosphere as well as about the shallow subsurface for exploration purposes. The resolution of these seismic data is highly appreciated; however they are logistically complex and expensive to acquire, and their geographical coverage is limited. Therefore, it is essential to make the most of the data that have already been acquired. The collation and dissemination of seismic open-access data are then key to promote accurate and innovative research and to enhance new interpretations of legacy data. This work presents the Seismic DAta REpository (SeisDARE), which is, to our knowledge, one of the first comprehensive open-access online databases that stores seismic data registered with a permanent identifier (DOI). The datasets included here are openly accessible online and guarantee the FAIR (findable, accessible, interoperable, reusable) principles of data management, granting the inclusion of each dataset in a statistics referencing database so its impact can be measured. SeisDARE includes seismic data acquired in the last 4 decades in the Iberian Peninsula and Morocco. These areas have attracted the attention of international researchers in the fields of geology and geophysics due to the exceptional outcrops of the Variscan and Alpine orogens and wide foreland basins, the crustal structure of the offshore margins that resulted from a complex plate kinematic evolution, and the vast quantities of natural resources contained within. This database has been built thanks to a network of national and international institutions, promoting a multidisciplinary research and is open for international data exchange and collaborations. As part of this international collaboration, and as a model for inclusion of other global seismic datasets, SeisDARE also hosts seismic data acquired in Hardeman County, Texas (USA), within the COCORP project (Consortium for Continental Reflection Profiling). SeisDARE aims to make easily accessible old and recently acquired seismic data and to establish a framework for future seismic data management plans. SeisDARE is freely available at (a detailed list of the datasets can be found in Table ), bringing endless research and teaching opportunities to the scientific, industrial, and educational communities.

2011

Seismology entirely depends on international co-operation. Only the accumulation of large sets of compatible high quality data in standardized formats from many stations and networks around the globe and over long periods of time will yield sufficiently reliable long-term results in event localization, seismicity rate and hazard assessment, investigations into the structure and rheology of the Earth's interior and other priority tasks in seismological research and applications.

2003

1] P S converted waves observed near Ancona on the Adriatic coast of central Italy, as revealed by teleseismic receiver functions (RFs), vary with earthquake backazimuth and epicentral distance in a manner consistent with a 1-D anisotropic seismic structure. Using reflectivity calculations, we develop a profile of anisotropic seismic velocity through the Adriatic lithosphere at this locality. We infer crustal thickness of $45 km. Anisotropy within the crust appears at $15-km depth, suggesting a decollement between the subducting Adriatic lithosphere and the overriding crustal wedge. Lineation of inferred rock fabric is compatible with simple shear in ENE-WSW direction. In the upper mantle, we infer an anisotropic layer at 80-90 km depth. If caused by olivine crystals alignment, the nearly north-south lineation of the inferred rock fabric would be consistent with some nearby shear-wave splitting observations. This anisotropic layer may be related to mantle deformation induced by the rollback of Adriatic lithosphere. INDEX TERMS: 7203 Seismology: Body wave propagation; 7218 Seismology: Lithosphere and upper mantle; 8102 Tectonophysics: Continental contractional orogenic belts. Citation: Levin, V.

2008

This centrality of Seismology engages multiple U.S. Federal agencies in supporting the discipline, including the NSF, the United States Geological Survey (USGS), the National Oceanic and Atmospheric Administration (NOAA), the Department of Energy (DOE), the Department of Defense (DoD), the Federal Emergency Management Agency (FEMA), and the National Aeronautics and Space Administration (NASA). This diversity of supporting agencies has benefited the discipline immensely, and reflects the multi-use nature of seismological data. U.S. Seismology is deeply engaged in international activities such as the International Monitoring System (IMS) of the Comprehensive (Nuclear) Test Ban Treaty Organization (CTBTO), and the Global Earth Observations System of Systems (GEOSS), placing the discipline in high-level, politically influential roles. One sign of a healthy scientific enterprise is the degree to which it is undergoing major advances and paradigm shifts. As manifest in this report, Seismology is a dynamic and energized field, with a continually expanding portfolio of important contributions. Examples of recent transformative developments in the discipline include the following: • Creation of the open-access seismic data repository of the Incorporated Research Institutions for Seismology (IRIS) Data Management System (DMS). This facility, housing terabytes of data freely delivers seismic data to the entire world, an approach being emulated internationally. Providing all researchers with access to data enables proliferating discoveries and societal applications. (FIG. 1. NEAR HERE) • The discovery of coherent information contained in recorded seismic 'noise'. The background vibrations of the Earth contain information about sources and structures that was not recognized until recently. Processing of multiple station data allows every data byte to be used for scientific application, and entirely new approaches to structural studies and investigations of changes in the environment have ensured. (FIG. 2. NEAR HERE)

Seismological Research Letters, 2021

Seismic bulletins, with trustworthy phase picks, origin times, and source locations are key for regional seismic studies, such as travel-time (TT) tomography, attenuation tomography, and anisotropy studies. To lay the groundwork for such studies in Israel, we revised the seismic bulletin of Israel and the surrounding area and obtained a trustworthy TT data set. From the earthquake and explosion bulletins of the Geophysical Institute of Israel, we compiled a starting data set of about 123,000 earthquakes and explosions that occurred during the past 40 yr. After screening out the poorly recorded events, we were left with a data set of ∼ 38,000 well-recorded events. We then revised the remaining data set in two consecutive steps. In the first, we reviewed and updated station metadata, including changes in station metadata parameters over time. In the second step, we jointly relocated a list of selected seismic events, using the Bayesian hierarchical location software package (BayesLoc) of Myers et al. (2007) that performs joint relocation of multiple events. We observed striking dissimilarities between the spatial distributions of the newly relocated catalogue and the initial locations. Although the depth distribution of the starting catalogue is trimodal with peaks at 0, 5, and 10 km, the distribution in this study is unimodal, with a broad peak between 7.5 and 12.5 km. By differencing the observed arrival times and the origin times obtained through relocation with BayesLoc, we obtained a revised TT database that consists of 261,336 Pg, 132,876 Pn, 114,816 Sg, and 60,394 Sn arrivals, from a set of 30,458 jointly relocated seismic sources. We compared prerevision and postrevision TTs as a function of epicentral distance and concluded that the revised data set contains far fewer outliers and inconsistencies than the original data set. The revised TT data set may be used for seismic studies, such as TT tomography, attenuation tomography, and anisotropy studies.

Annals of Geophysics, 2023

This special issue of Annals of Geophysics "Seismic anisotropy and shear-wave splitting: Achievements and perspectives" originates from a session (S10) of the 37 th General assembly of the European Seismological commission ESC 2021 Conference which was planned to take place on 21 September 2021, in Corfu Greece, but due to the Covid19 pandemic was Virtual. The main theme of the session and of this special issue was the crucial role of seismic anisotropy in investigating the Earth's interior from the upper crust to the inner core. Shear-wave splitting, one of the most effective ways to study seismic anisotropy, can identify the properties and the geodynamics of the upper mantle, and identify the presence of fluid-saturated microcracks, oriented according to the stress regime, in the upper crust. Azimuthal anisotropy and radial anisotropy can be assessed from earthquake or ambient noise recordings to detect the seismic layered features and to rebuild the 3D seismic structure.

Earth and Space Science, 2020

A data set of earthquake hypocenters and associated traveltime residuals for seismic phases recorded by seismograph stations globally is an essential starting point for most studies of global seismicity and Earth structure. Such data sets have been produced in various forms by national and international agencies since the beginning of instrumental seismology at the turn of the twentieth century. We have reprocessed the comprehensive data used to produce the routinely distributed bulletins of the International Seismological Centre (ISC) since 1964 to construct a new refined data set of hypocenters with improved focal depths and phase residuals. This data set, called ISC‐EHB, is used to reveal features of the seismotectonic zones in downgoing slabs in greater detail than previously routinely available.

Geophysical Research Letters, 2001

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

2013

Journal of Geophysical Research, 2008

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.