The probability of large earthquakes cannot be calculated from seismicity rates

2020 ◽  
Author(s):  
Max Wyss
Keyword(s):  
Seismic Waves ◽  
Slip Rate ◽  
Strike Slip ◽  
Magnitude Scale ◽  
Recurrence Time ◽  
Normal Faults ◽  
Earthquake Probability ◽  
San Andreas ◽  
Seismicity Rates ◽  
Large Earthquakes

<p>The hypothesis that extrapolation of the Gutenberg-Richter (GR) relationship allows estimates of the probability of large earthquakes is incorrect. For nearly 200 faults for which the recurrence time, T<sub>r</sub> (1/probability of occurrence), is known from trenching and geodetically measured deformation rates, it has been shown that T<sub>r</sub> based on seismicity is overestimated typically by one order of magnitude or more. The reason for this is that there are not enough earthquakes along major faults. In some cases there are too few earthquakes for the fault to be mapped based on seismicity. Some examples are the following rupture segments of great faults: the 1717 Alpine Fault, the 1856 San Andreas, the 1906 San Andreas, the 2001 Denali earthquakes, for which geological Tr are 100 years to 300 years and seismicity T<sub>r</sub> are 10,000 to 100,000 years. In addition, the hypothesis leads to impossible results when one considers the dependence of the b-value on stress. It has been shown that thrusts, strike-slip and normal faults have low, intermediate and high b-values, respectively. This implies that, regardless of local slip rates, the probability of large earthquakes predicted by the hypothesis is high, intermediate and low in thrust, strike-slip, and normal faulting, respectively. Measurements of recurrence probability show a different dependence: earthquake probability depends on slip rate. Finally, the hypothesis predicts different probabilities for large earthquakes, depending on the magnitude scale used. For the 1906 rupture segment, the difference in probability of an M8 earthquake is approximately a factor of 50, using the two available catalogs. Various countries measure earthquake magnitude on their own scale that is intended to agree with the M<sub>L</sub> scale of California or the M<sub>S</sub> scale of the USGS. However, it is not trivial to match a scale that is valid for a different region with different attenuation of seismic waves. As a result, some regional M-scales differ from the global M<sub>S</sub> scale, which yields different T<sub>r</sub> for the same Mmax in the same region, depending on whether the global or local magnitude scale is used. Based on the aforementioned facts, the hypothesis that probabilities of large earthquakes can be estimated by extrapolating the GR relationship has to be abandoned.</p>

Trench investigations through the trace of the 1980 El Asnam thrust fault: Evidence for paleoseismicity

1988 ◽  
Vol 78 (2) ◽  
pp. 979-999
Author(s):  
M. Meghraoui ◽  
H. Philip ◽  
F. Albarede ◽  
A. Cisternas
Keyword(s):  
Late Holocene ◽  
Slip Rate ◽  
Thrust Fault ◽  
Recurrence Time ◽  
Normal Faults ◽  
Tectonic Event ◽  
Vertical Movements ◽  
Radiocarbon Dates ◽  
Flood Deposits ◽  
Large Earthquakes

Abstract During the EI Asnam earthquake of 10 October 1980 (Ms = 7.3), a clear active thrust fault with left-lateral offset was observed. Three trenches have been excavated across this fault in order to determine slip rate and recurrence intervals between large earthquakes, and thus reconstruct its past activity. Exposure I was excavated in the flood area created in 1980 by a pressure ridge across the Cheliff and Fodda Rivers. Six flood deposits (silty-sandy and muddy horizons) alternating with paleosoils appear in this exposure; they are affected by normal faults associated with the main thrust fault. Assuming that every flood deposit results from a tectonic event of magnitude greater than 7, we can correlate previous flood deposits with these events. Exposures II and III display thrust faults displacing different paleosoils. We propose a sequence of reconstructions based on the thickness of the various deposits and the dip-slip of each tectonic event. The Late Holocene slip rate is 0.65 mm/yr for the dip-slip and 0.46 mm/yr for each of the horizontal and the vertical movements. Radiocarbon dates of coseismic movements indicate a rather irregular seismic activity during the past 7000 yr. Two sequences of large earthquakes around 4000 yr B.P. and around the modern age are separated with a period of quiescence. The average Late Holocene recurrence interval of large earthquakes is 1061 yr; however, during the active faulting episodes, the recurrence time varies from approximately 300 to 500 yr.

scholarly journals A revised position for the primary strand of the Pleistocene-Holocene San Andreas fault in southern California

2021 ◽  
Vol 7 (13) ◽  
pp. eaaz5691
Author(s):  
Kimberly Blisniuk ◽  
Katherine Scharer ◽  
Warren D. Sharp ◽  
Roland Burgmann ◽  
Colin Amos ◽  
...  
Keyword(s):  
Los Angeles ◽  
Southern California ◽  
San Andreas Fault ◽  
Slip Rate ◽  
Large Magnitude ◽  
Slip Rates ◽  
San Andreas ◽  
The Pacific ◽  
Large Earthquakes ◽  
Dependent Probability

The San Andreas fault has the highest calculated time-dependent probability for large-magnitude earthquakes in southern California. However, where the fault is multistranded east of the Los Angeles metropolitan area, it has been uncertain which strand has the fastest slip rate and, therefore, which has the highest probability of a destructive earthquake. Reconstruction of offset Pleistocene-Holocene landforms dated using the uranium-thorium soil carbonate and beryllium-10 surface exposure techniques indicates slip rates of 24.1 ± 3 millimeter per year for the San Andreas fault, with 21.6 ± 2 and 2.5 ± 1 millimeters per year for the Mission Creek and Banning strands, respectively. These data establish the Mission Creek strand as the primary fault bounding the Pacific and North American plates at this latitude and imply that 6 to 9 meters of elastic strain has accumulated along the fault since the most recent surface-rupturing earthquake, highlighting the potential for large earthquakes along this strand.

Late Pleistocene extension and strike-slip in the Dead Sea Basin

2004 ◽  
Vol 141 (5) ◽  
pp. 565-572 ◽  
Author(s):  
YUVAL BARTOV ◽  
AMIR SAGY
Keyword(s):  
Internal Structure ◽  
Slip Rate ◽  
Dead Sea ◽  
Strike Slip ◽  
Normal Faults ◽  
Small Scale ◽  
Dead Sea Basin ◽  
Pull Apart Basin ◽  
Western Border ◽  
The Dead

A newly discovered active small-scale pull-apart (Mor structure), located in the western part of the Dead Sea Basin, shows recent basin-parallel extension and strike-slip faulting, and offers a rare view of pull-apart internal structure. The Mor structure is bounded by N–S-trending strike-slip faults, and cross-cut by low-angle, E–W-trending normal faults. The geometry of this pull-apart suggests that displacement between the two stepped N–S strike-slip faults of the Mor structure is transferred by the extension associated with the normal faults. The continuing deformation in this structure is evident by the observation of at least three deformation episodes between 50 ka and present. The calculated sinistral slip-rate is 3.5 mm/yr over the last 30 000 years. This slip rate indicates that the Mor structure overlies the currently most active strike-slip fault within the western border of the Dead Sea pull-apart. The Mor structure is an example of a small pull-apart basin developed within a larger pull-apart. This type of hierarchy in pull-apart structures is an indication for their ongoing evolution.

Multisegment Rupture Hazard Modeling along the Xianshuihe Fault Zone, Southeastern Tibetan Plateau

2020 ◽  
Author(s):  
Jia Cheng ◽  
Thomas Chartier ◽  
Xiwei Xu
Keyword(s):  
Slip Rate ◽  
Historical Earthquakes ◽  
Input Constraints ◽  
Ground Acceleration ◽  
Slip Rates ◽  
Fault Slip Rates ◽  
Seismicity Rates ◽  
Xianshuihe Fault Zone ◽  
Large Earthquakes ◽  
Southern Section

Abstract The Xianshuihe fault is a remarkable strike-slip fault characterized by high slip rate (∼10  mm/yr) and frequent strong historical earthquakes. The potential for future large earthquakes on this fault is enhanced by the 2008 Mw 7.9 Wenchuan earthquake. Previous works gave little attention to the probabilities of multisegment ruptures on the Xianshuihe fault. In this study, we build five possible multisegment rupture combination models for the Xianshuihe fault. The fault slip rates and historical earthquakes are used as input constraints to model the future seismicity on the fault segments and test whether the rupture combination models are appropriate. The segment combination model, based essentially on historical ruptures, has produced the seismicity rates most consistent with the historical records, although the model with ruptures on both the entire northern section and southern section should also be considered. The peak ground acceleration values with a return period of 475 yr calculated using the modeled rates on the Xianshuihe fault for both two models are on average larger than the values of the China Seismic Ground Motion Parameters Zonation Map.

The longer it has been since the last earthquake, the longer the expected time till the next?

1989 ◽  
Vol 79 (5) ◽  
pp. 1439-1456
Author(s):  
Paul M. Davis ◽  
David D. Jackson ◽  
Yan Y. Kagan
Keyword(s):  
Affirmative Answer ◽  
Recurrence Time ◽  
Earthquake Risk ◽  
Parameter Estimates ◽  
Earthquake Probability ◽  
Expected Time ◽  
San Andreas ◽  
Estimated Risk ◽  
Characteristic Earthquakes ◽  
Variance Estimates

Abstract We adopt a lognormal distribution for earthquake interval times, and we use a locally determined rather than a generic coefficient of variation, to estimate the probability of occurrence of characteristic earthquakes. We extend previous methods in two ways. First, we account for the aseismic period since the last event (the “seismic drought”) in updating the parameter estimates. Second, in calculating the earthquake probability we allow for uncertainties in the mean recurrence time and its variance by averaging over their likelihood. Both extensions can strongly influence the calculated earthquake probabilities, especially for long droughts in regions with few documented earthquakes. As time passes, the recurrence time and variance estimates increase if no additional events occur, leading eventually to an affirmative answer to the question in the title. The earthquake risk estimate begins to drop when the drought exceeds the estimated recurrence time. For the Parkfield area of California, the probability of a magnitude 6 event in the next 5 years is about 34 per cent, much lower than previous estimates. Furthermore, the estimated 5-year probability will decrease with every uneventful year after 1988. For the Coachella Valley segment of the San Andreas Fault, the uncertainties are large, and we estimate the probability of a large event in the next 30 years to be 9 per cent, again much smaller than previous estimates. On the Mojave (Pallett Creek) segment the catalog includes 10 events, and the present drought is just approaching the recurrence interval, so the estimated risk is revised very little by our methods.

scholarly journals Extension and slip rate partitioning in NW Iran constrained by GPS measurements

2011 ◽  
Vol 1 (4) ◽  
pp. 286-304 ◽  
Author(s):  
A. Rastbood ◽  
B. Voosoghi
Keyword(s):  
Large Scale ◽  
Slip Rate ◽  
Strike Slip ◽  
Fault System ◽  
Arabian Plate ◽  
Normal Faults ◽  
Gps Data ◽  
Gps Measurements ◽  
Nw Iran ◽  
Himalayan Mountain

Extension and slip rate partitioning in NW Iran constrained by GPS measurementsConvergence of 22±2 mm yr-1 between the northward motion of the Arabian Plate relative to Eurasia at N8° ±5° E is accommodated by a combination of thrust and strike-slip faults in different parts of Iran. Dislocation modeling is used to examine the GPS data for this part of the Alpine-Himalayan mountain belt with more concentration in NW Iran. First, the vectors due to known Arabia-Eurasia rotation are reproduced by introducing structures that approximate the large-scale tectonics of the Middle East. Observed features of the smaller scale fault system are then progressively included in the model. Slip rate amplitudes and directions adjusted to fit available GPS data. Geological evidences show strike-slip and reverse-slip faulting in NW Iran, but GPS data show normal faults in this region too. By slip partitioning we propose four locations for normal faults based on extensions observed by GPS data. Slip rate values were estimated between 2 ~ 5 mm/yr for proposed normal faults. Our modeling results prove that the NW Iran is not only affected by Arabia-Eurasia collision but also contributes in the subduction motion of the South Caspian and Kura basins basement beneath the Apsheron-Balkhan sill and the Great Caucasus respectively.

Return Times of Large Earthquakes Cannot Be Estimated Correctly from Seismicity Rates: 1906 San Francisco and 1717 Alpine Fault Ruptures

2020 ◽  
Vol 91 (4) ◽  
pp. 2163-2169
Author(s):  
Max Wyss
Keyword(s):  
United States ◽  
San Francisco ◽  
San Andreas Fault ◽  
Return Time ◽  
Local Seismicity ◽  
Return Times ◽  
Alpine Fault ◽  
San Andreas ◽  
Seismicity Rates ◽  
Large Earthquakes

Abstract The unproven assumption that the Gutenberg–Richter (GR) relationship can be extrapolated to estimate the return time, Tr (1/probability of occurrence), of major and large earthquakes has been shown to be incorrect along 196 faults, so far. Here, two more examples of great, well-known faults that do not produce enough earthquakes to fulfill the hypothesis are analyzed. The 300 km section of the San Andreas fault, California, United States, that ruptured in 1906 in the M 8 San Francisco earthquake, produced 200 earthquakes with M≥2 in the last 52 yr, when about 250,000 such events are expected according to the hypothesis. Along a 250 km section that broke in an M 7.9 earthquake in 1717 along the Alpine fault, New Zealand, the number of reported M≥3.6 earthquakes during the last 34 yr was 100, when about 6000 would be expected, based on the hypothesis. Extrapolating the GR relationships for these two fault segments, one estimates Tr of mainshocks of M 8 to be about 10,000 and 100,000 for the 1717 and 1906 ruptures, respectively. Regardless of choice of analysis parameters, this is by factors of 10–400 larger than estimates based on paleogeology, tectonics, and geodesy. In addition, second catalogs for each case yield estimates of probabilities for M 8 earthquakes along the 1717 and 1906 rupture segments that differ by factors of about 2 and 80 (between 5000 and 98,000 yr) from the first respective catalogs. It follows that the probability of large earthquakes cannot be estimated correctly based on local seismicity rates along major faults.

scholarly journals Evidence for temporal clustering of large earthquakes in the wellington region from computer models of seismicity

1998 ◽  
Vol 31 (1) ◽  
pp. 24-32 ◽  
Author(s):  
Russell Robinson ◽  
Rafael Benites ◽  
Russ Van Dissen
Keyword(s):  
Slip Rate ◽  
Strike Slip ◽  
Seismic Behaviour ◽  
Plate Interface ◽  
Slip Rates ◽  
Elastic Interactions ◽  
Temporal Clustering ◽  
Engineering Insurance ◽  
Event Times ◽  
Large Earthquakes

Temporal clustering of large earthquakes in the Wellington region, New Zealand, has been investigated with a computer model that generates long synthetic seismicity catalogues. The model includes the elastic interactions between faults. Faults included in the model, besides the subduction thrust between the Australian and Pacific plates, are segments of the four major strike-slip faults that overlie the plate interface (Wairarapa, Wellington, Ohariu, and Wairau faults). Parameters of the model are adjusted to reproduce the geologically ohserved slip rates of the strike-slip faults. The seismic slip rate of the subduction thrust, which is unknown, is taken as 25% of the maximum predicted by the plate tectonic convergence rate, and its position fixed according to recent geodetic results. For comparison, the model was rerun with the elastic interactions suppressed, corresponding to the usual approach in the calculation of seismic hazard where each fault is considered in isolation. Considering earthquakes of magnitude 7.2 or more ("characteristic" events in the sense that they rupture most of a fault plane). the number of short (0-3 years) inter-event times is much higher with interactions than for the corresponding case without interactions (46% vs. 2% or all inter-event times). This reduces to 9% vs. 2% if the subduction thrust is removed from the models. Paleoseismic studies of the past seismic behaviour of the subduction thrust are clearly needed if the degree of clustering is to be tightly constrained. Although some other aspects of our model can he improved in future, we think that the probability of significant short-term clustering of large events, normally neglected in hazard studies, is very high. This has important implications for the engineering, insurance and emergency response communities.

scholarly journals KASTORIA “BLIND” ACTIVE FAULT: HAZARDOUS SEISMOGENIC FAULT OF THE NW GREECE

2017 ◽  
Vol 43 (1) ◽  
pp. 442
Author(s):  
Ch. P. Metaxas ◽  
N.S. Lalechos ◽  
S.N. Lalechos
Keyword(s):  
Hazard Analysis ◽  
Slip Rate ◽  
Recurrence Time ◽  
Seismic Cycle ◽  
Seismogenic Fault ◽  
Ground Shaking ◽  
Seismicity Parameters ◽  
River Bed ◽  
Seismicity Rates ◽  
Eastern Edge

The Aliakmon river bed, as well as a series of certain parallel narrow grabens, striking NW-SE are filled with Neogene-Quaternary deposits; thus showing the existence of the covered, “blind”, fault zone, which borders the Eastern edge of Meso-Hellenic Trench and passes in close vicinity to the Kastoria town. Distribution of earthquakes epicentres (M≥4.0, for the period of 1930-2009) along this segmented rupture zone, proves the existence at depth of an active seismogenic fault which has generated some strong earthquakes in the past: 1709, M = 6.0; 1812, M = 6.5 and 1894, M = 6.1 (~ 100-year Recurrence Time events). The calculations of Lapsed Rate characterizing the stage of the fault seismic cycle (LR = 115%) show that the active Kastoria fault could be in a pre-seismic stage of its seismic cycle. Applying the seismicity rates model (time-independent Gutenberg-Richter recurrence model) and using the fault seismicity parameters, obtained inside the fault influence zone, as input in EZ-FRISK® software, the Probabilistic Seismic Hazard Analysis has been carried out for the area of Kastoria town. The results show that calculated magnitude for event with 100- year recurrence time is ~6.1, which correspond to the magnitude of three events, occurred at the fault during the last 300 years (corresponding average slip rate . 3 mm/year). As the calculated Hazard Curve shows, the event of that range could give ground shaking in the Kastoria town in the order of 0.625 g at the spectral period of 0.3 sec.

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