Earthquake Science and Seismic Risk Reduction

Francesco Mulargia

doi:10.1007/978-94-010-0041-3

Outline

Earthquake Science and Seismic Risk Reduction

Francesco Mulargia

2003

https://doi.org/10.1007/978-94-010-0041-3

visibility

…

description

14 pages

link

1 file

Abstract
AI

The study explores the fundamental principles of earthquake science and methodologies for seismic risk reduction. It discusses models of earthquake mechanics, the significance of scaling laws, the energy balance during seismic events, and the importance of characterizing and predicting earthquakes through complex systems theories. The research addresses both theoretical models and practical implications for improving earthquake preparedness and response.

FAQs

What explains the limitations in predicting individual large earthquakes?add

The paper reveals that our understanding of earthquake physics is insufficient for deterministic predictions, as highlighted by the complex nature of lithospheric dynamics.

How does the lithosphere respond to stress buildup over geological timescales?add

The study finds that the lithosphere releases strain energy primarily through brittle failure, resulting in earthquakes rather than viscous deformation, which is prevalent in the mantle.

What role do building codes play in seismic risk reduction?add

The findings demonstrate that enforcing modern building codes significantly decreases risks; experiences from Greece and Turkey show substandard construction as a primary cause of casualties during earthquakes.

Why is there a mismatch between geological and human time scales in earthquake studies?add

The paper discusses that while mantle convection operates on scales of 10^8 years, we have only about 100 years of instrumental data, hampering our understanding of earthquake cycles.

How can geological studies improve our understanding of seismic hazards?add

The text emphasizes that geological studies extending back 10,000 years can provide crucial historical context that enhances hazard estimation methodologies.

References (41)

Space-time history of faulting . . . . . . . . . . . . . . . 44
3 Scaling laws for earthquakes . . . . . . . . . . . . . . . . . . . . 46 2.3.1 The Gutenberg-Richter law . . . . . . . . . . . . . . . . . 46 2.3.2 Empirical roots of the Gutenberg-Richter law . . . . . . . 47 2.3.3 Moment-frequency relation . . . . . . . . . . . . . . . . 48
4 The elastic rebound model and its successors . . . . . . . . . . . 52 2.4.1 The time-and slip-predictable models . . . . . . . . . . . 53 2.4.2 The seismic gap hypothesis . . . . . . . . . . . . . . . . 55 2.4.3 The characteristic earthquake model . . . . . . . . . . . . 56
5 Nucleation or not? . . . . . . . . . . . . . . . . . . . . . . . . . . 58 2.5.1 Is there any evidence for a nucleation phase? . . . . . . . 58 2.5.2 Models of a hypothetical preparatory process . . . . . . . 59 2.5.3 Theoretical models . . . . . . . . . . . . . . . . . . . . . 60
6 What is an earthquake? Fracture, slip or both? . . . . . . . . . . . 62 2.6.1 Laboratory-based hypotheses . . . . . . . . . . . . . . . . 62 2.6.2 Stick-slip friction . . . . . . . . . . . . . . . . . . . . . . 63 2.6.3 Fracture mechanics . . . . . . . . . . . . . . . . . . . . . 68 2.6.4 Damage mechanics . . . . . . . . . . . . . . . . . . . . . 69
7 Stress: the basic yet unknown quantity . . . . . . . . . . . . . . . 73 2.7.1 Stress in the Earth's crust . . . . . . . . . . . . . . . . . . 74
8 Earthquake energy balance . . . . . . . . . . . . . . . . . . . . . 77 2.8.1 Earthquake energy function . . . . . . . . . . . . . . . . 77 2.8.2 Earthquakes as a three stage process . . . . . . . . . . . . 82 2.8.3 The size of the earthquake . . . . . . . . . . . . . . . . . 85
9 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 3 Physics of complex systems and earthquakes 102
1 Phase transitions, criticality, and self-similarity . . . . . . . . . . 103
1.1 Subcriticality and supercriticality . . . . . . . . . . . . . 108
1.2 Universality . . . . . . . . . . . . . . . . . . . . . . . . . 108
2 Scale invariance: the analytical approach . . . . . . . . . . . . . . 109
3 Scale invariance: the geometrical approach . . . . . . . . . . . . 111 3.3.1 Measuring an object's fractal dimension . . . . . . . . . . 112 3.3.2 Multifractals . . . . . . . . . . . . . . . . . . . . . . . . 114
3.3 The empirical origin of fractality . . . . . . . . . . . . . . 115 3.3.4 Deterministic low-dimensional chaos: hope for predictabil- ity? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
4 Characterizing scale-invariant systems . . . . . . . . . . . . . . . 117 3.4.1 Log-log plots . . . . . . . . . . . . . . . . . . . . . . . . 118 3.4.2 Wavelets . . . . . . . . . . . . . . . . . . . . . . . . . . 118
5 Modeling scale invariant systems . . . . . . . . . . . . . . . . . . 119
3 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Earthquake prediction and public policy 8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.1 Why should we care now? . . . . . . . . . . . . . . . . .
1.2 Ethical considerations . . . . . . . . . . . . . . . . . . .
1.3 Definitions of earthquake prediction . . . . . . . . . . . .
1.4 Proposals for earthquake prediction research . . . . . . .
2 Views of social scientists . . . . . . . . . . . . . . . . . . . . . .
2.1 Report of NAS Panel in 1975 . . . . . . . . . . . . . . .
2.2 Social science research . . . . . . . . . . . . . . . . . . .
2.3 Costs and benefits of short-term earthquake prediction . .
U.S. earthquake prediction program . . . . . . . . . . . . . . . .
3.1 Current Federal and State laws . . . . . . . . . . . . . . .
3.2 NEPEC . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3 Parkfield earthquake prediction experiment . . . . . . . .
Japan's earthquake prediction program . . . . . . . . . . . . . . .
4.1 Long-term forecast of the 'Tokai earthquake' . . . . . . .
4.2 System for short-term prediction . . . . . . . . . . . . . .
4.3 Public perception . . . . . . . . . . . . . . . . . . . . . .
5 Public reactions to predictions . . . . . . . . . . . . . . . . . . .
5.1 Codes of practice for earthquake prediction . . . . . . . .
5.2 Publicly announced predictions . . . . . . . . . . . . . .
5.3 Common features . . . . . . . . . . . . . . . . . . . . . .
5.4 Countermeasures . . . . . . . . . . . . . . . . . . . . . .
6 Discussion and conclusion . . . . . . . . . . . . . . . . . . . . .
7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Forecasting earthquakes implies that there are time-varying processes, which depend on the changing conditions deep in the Earth's crust prior to major seismic activity. These processes may be linearly or non-linearly correlated. In seismology, the research has traditionally been centered on mechanical variables, including precursory ground deformation (revealing the build-up of stress deep below) and on prior seismic events (past earthquakes may be related to or even trigger future earthquakes). Since the results have been less than convincing, there is a general consensus in the geoscience community that earthquake forecasting on time scales comparable to meteorological forecasts are still quite far in the future, if ever attainable. 1.4 Solid state physics: is it the key? Much before and well after seismology developed into a hard science, mainly based on mechanical concepts of static and dynamic deformation of materials, solid state physics may have provided another way to consider the preparatory stages to large earthquake occurrences (for instance, one can trace the connection of earthquakes and electromagnetic phenomena back to the papers of Shida, 1886, and Milne, 1890). Countless reports of precursory phenomena have been accumulated through time, first witnessing visual observations, then recorded by an ever increasing number of ground stations or remote satellites. Those precursory signals are thought to reflect the time-varying processes associated with the slow tectonic stress accumulation in the Earth's crust. Such reported pre-seismic earthquake precursors recorded on the ground or from space are compiled in Table 1 and concern very diverse categories such as variations of the magnetic field, electromagnetic fluctuations over various frequency bands, gas emanation from the ground, changes of ionospheric properties, earthquake lights, night glows, up to the controversial reports of weird behavior of domestic or wild animals. Table 1: types of anomalous signals usually reported prior to seismic events. Unfortunately, the seismological community never considered such precursors as being reliable or meaningful, which led to an unfortunate disconnection, if not a definitive dialog breakage, between the two communities. The main concerns and criticisms raised within the seismological community include: (i) non-seismic precursors were not properly tested in a statistical sense, since the published Satellites observations Thermal Infrared (TIR) anomalies Total Electron Content (TEC) anomalies Changes in ionospheric ion concentrations Ionospheric electric field turbulences Atmospheric Gravity Waves (AGW) CO release from the ground Ozone formation at ground level VLF attenuation due to air ionization Mesospheric lightning Lineaments in the VIS-NIR Ground stations observations Medium-term magnetic field variations ULF emission from within the Earth crust Tree potentials and ground potentials Soil conductivity changes Groundwater chemistry changes Trace gas such as CO release from the ground Radon emanation from the ground Positive and negative air ionization Sub-ionospheric VLF/ELF propagation Nightglow amd chromatic shifts

The physical mechanism of the anthropogenic triggering of large earthquakes on active faults is studied on the basis of experimental phenomenology, i.e., that earthquakes occur on active tectonic faults, that crustal stress values are those measured in situ and, on active faults, comply to the values of the stress drop measured for real earthquakes, that the static friction coefficients are those inferred on faults, and that the effective triggering stresses are those inferred for real earthquakes. Deriving the conditions for earthquake nucleation as a time-dependent solution of the Tresca-Von Mises criterion applied in the framework of poroelasticity yields that active faults can be triggered by fluid overpressures , 0.1 MPa. Comparing this with the deviatoric stresses at the depth of crustal hypocenters, which are of the order of 1-10 MPa, we find that injecting in the subsoil fluids at the pressures typical of oil and gas production and storage may trigger destructive earthquakes on active faults at a few tens of kilometers. Fluid pressure propagates as slow stress waves along geometric paths operating in a drained condition and can advance the natural occurrence of earthquakes by a substantial amount of time. Furthermore, it is illusory to control earthquake triggering by close monitoring of minor ''foreshocks'', since the induction may occur with a delay up to several years. T he central role of fluids in seismic faulting is known in all stages of the earthquake cycle, i.e., in the nucleation processes, in the dynamic propagation and in the post-seismic evolution. Namely, pore fluid pressure affects the whole earthquake process starting from fault nucleation 1,2 , continues through thermally-activated pressurization 3-7 and mechanical lubrication 8,9 , and finally plays a role in triggering aftershocks 10-14. Interest on the first step of the process (fault reactivation and rupture nucleation) has been recently revived by several cases of human activities, which are indicted for having induced destructive earthquakes. Davies et al. 15 compiled a list of 190 possible examples of induced earthquakes, with magnitude spanning between 1.0 and 7.9, connected with mining, artificial reservoir impoundment, geothermal operations 16,17 , oil and gas field production and hydraulic fracturing (i.e., fracking). Most earthquakes induced by anthropogenic activities concern small magnitude events (M , 3.0) located in the vicinity of the activities themselves 18,19. Here we are not interested in such earthquakes, which generally constitute more a nuisance than a real danger. Indeed, we are interested in the other type of induced seismicity, which regards large events (M. 5.5) on nearby active tectonic faults, at a distance up to a few tens of kilometers 20,21. This type of induction is appropriately termed triggered (or activated) seismicity 22 , since human activities provide the tiny-but fundamental-input to a system which is independently close to instability. A small action produces a large reaction, just as the modest pressure of a finger on a gun trigger releases the large explosive energy stored in the propellant. Such a type of induced seismicity has been so far mostly associated with the impoundment of artificial water reservoirs, but occasionally also with gas and oil production. Triggered seismicity is the most important and dangerous type of induced seismicity, and should not be confused with its stablemate, simply called induced seismicity; the latter is commonly associated with drilling or hydrofracture and generally implies large local stresses, but small earthquakes. In fact, to induce fresh fracture in the bulk rock the applied stresses must be, by definition, equal to those determined by hydrofracture techniques. However, event size is small because these large stresses are spatially concentrated and can only induce fracture on small volumes of rock. On the contrary, triggered seismicity involves large tectonic structures, where the stress has been independently accumulating to a near failure conditions by the internal Earth's dynamics 23,24 , with the human activity providing only the ''last straw''. Although the unequivocal discrimination between naturally occurring and man-triggered earthquakes is difficult 25,26 , there exist some hardly questionable cases. The first documented case of reservoir-triggered seismicity occurred in 1932 in Algeria's Oued Fodda Dam. Another prominent example is provided by the realization of the Koyna Dam, India, which was followed in 1967 by the M6.

Earthquake Science and Seismic Risk Reduction

Sign up for access to the world's latest research

AbstractAI

FAQs

Related papers

References (41)

Related papers

Related topics

Cited by

Abstract
AI