Probability Of Large Earthquakes Research Articles

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

AbstractThe 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.

Variation of singularity of earthquake-size distribution with respect to tectonic regime

Frequency–size relation of earthquakes in a region can be approximated by the Gutenberg-Richter law (GR). This power-law model involves two parameters: a-value measuring seismic activity or earthquake productivity, and b-value describing the relation between frequencies of small and large earthquakes. The spatial and temporal variations of these two parameters, especially the b-value, have been substantially investigated. For example, it has been shown that b-value depends inversely on differential stress. The b-value has also been utilized as earthquake precursor in large earthquake prediction. However, the physical meaning and properties of b-value including its value range still remain as an open fundamental question. We explore the property of b-value from frequency–size GR model in a new form which relates average energy release and probability of large earthquakes. Based on this new form of GR relation the b-value can be related to the singularity index (1–2/3b) of fractal energy – probability power-law model. This model as applied to the global database of earthquakes with size M ≥ 5 from 1964 to 2015 indicates a systematic increase of singularity from earthquakes occurring on mid-ocean ridges, to those in subduction zones and in collision zones.

The 2011 M = 9.0 Tohoku oki earthquake more than doubled the probability of large shocks beneath Tokyo

AbstractThe Kanto seismic corridor surrounding Tokyo has hosted four to five M ≥ 7 earthquakes in the past 400 years. Immediately after the Tohoku earthquake, the seismicity rate in the corridor jumped 10‐fold, while the rate of normal focal mechanisms dropped in half. The seismicity rate decayed for 6–12 months, after which it steadied at three times the pre‐Tohoku rate. The seismicity rate jump and decay to a new rate, as well as the focal mechanism change, can be explained by the static stress imparted by the Tohoku rupture and postseismic creep to Kanto faults. We therefore fit the seismicity observations to a rate/state Coulomb model, which we use to forecast the time‐dependent probability of large earthquakes in the Kanto seismic corridor. We estimate a 17% probability of a M ≥ 7.0 shock over the 5 year prospective period 11 March 2013 to 10 March 2018, two‐and‐a‐half times the probability had the Tohoku earthquake not struck.

Probability for Simulating Future Earthquakes with Mw >=6.0 in Taiwan for Seismic Hazard for the Earthquake Catalog from 1900 to 2008

In this study, we use extreme value theory based on Gumbel‐equation derivations to estimate the Gutenberg–Richter a and b parameters for Taiwan. Data are from the augmented, homogenized (in terms of moment magnitude), historic catalog for Taiwan. The island is divided into grids of 0.2° latitude by 0.2° longitude, and Gumbel type 1 statistical analysis is applied. The values of a and b are then used to determine the probability of large earthquakes ( M w≥6.0) occurring at each grid. The results show two relatively high probability paths for large earthquakes, one extending from Hsinchu southward to Taichung, Chiayi, and Tainan in western Taiwan and the other from Ilan southward to Hualian and Taitung in eastern Taiwan, both of which are characterized by low b ‐values. It indicates that future earthquakes can be expected along these paths characterized by low b ‐values. Additionally, maximum peak ground acceleration and maximum peak ground velocity (determined from respective attenuation laws and a gridding regimen of 0.1° latitude by 0.1° longitude for Taiwan) follow similar paths to that of the low b ‐values.

On the reality of the 56-year cycle and the increased probability of large earthquakes for Petropavlovsk-Kamchatskii during the period 2008–2011 according to lunar cyclicity

A 56-year cyclicity in the occurrence of large Kamchatka earthquakes has been previously detected. This is another manifestation of the tendency for the timing of large Kamchatka earthquakes to be synchronized to the cycles related to the period To of rotation of the lunar nodes found by V.A. Shirokov in 1974. He identified cycles of 18.6 years = To and 6.2 years = To/3, while the period of the 56-year cycle is 3To. The genuineness of that phenomenon had to be revised in connection with the occurrence of a large (Mw = 7.8) earthquake in Kamchatka at the end of 1997, in violation of the 56-year cyclicity. It turned out that, even though the 56-year cycle has become less distinct after the 1997 event, the cyclicity itself has remained statistically significant. A byproduct is an updated forecast of earthquake hazard for Kamchatka. The update is necessary in view of the approaching hazardous period of 2008–2011. It is found that, assuming the validity of these empirical tendencies, the expected rate of large earthquakes off Kamchatka for the period of August 2008 to October 2011 will be four times as high as the long-term mean. We derive the first-ever estimate of future hazard in terms of felt intensity for specified soil conditions (the so-called average soil) at a specified site (the town of Petropavlovsk-Kamchatskii). For these soil conditions, the estimated probability of at least one shock of intensity VII or greater during the period specified above is equal to 0.39 ± 0.15. The expected rate of single events or sets of events with Mw ≥ 7.6 in Kamchatka during this period is 0.76 ± 0.25.

Use of Potential Foreshocks to Estimate the Short-term Probability of Large Earthquakes, Tohoku, Japan

This study seeks to construct a hazard function for earthquake probabilities based on potential foreshocks. Earthquakes of magnitude 6.5 and larger that occurred between 1976 and 2000 in an offshore area of the Tohoku region of northeast Japan were selected as events for estimating probabilities. Later occurrences of multiple events and aftershocks were omitted from targets. As a result, a total of 14 earthquakes were employed in the assessment of models. The study volume spans 300 km (East-West) × 660 km (North-South) × 60 km in depth. The probability of a target earthquake occurring at a certain point in time-space depends on the number of small earthquakes that occurred per unit volume in that vicinity. In this study, we assume that the hazard function increases geometrically with the number of potential foreshocks within a constrained space-time window. The parameters for defining potential foreshocks are magnitude, spatial extent and lead time to the point of assessment. The time parameter is studied in ranges of 1 to 5 days (1-day steps), and spatial parameters in 20 to 100 km (20-km steps). The model parameters of the hazard function are determined by the maximum likelihood method. The most effective hazard function examined was the following case: When an earthquake of magnitude 4.5 to 6.5 occurs, the hazard for a large event is increased significantly for one day within a 20 km radius surrounding the earthquake. If two or more such earthquakes are observed, the model expects a 20,000 times greater probability of an earthquake of magnitude 6.5 or greater than in the absence of such events.

Progress in Paleoseismology in Japan during the 1990s.

We review progress of geological and geomorphological approaches in paleoseismology in Japan during the this decade. We emphasize the growth of active fault studies since the 1995 Kobe earthquake. Two examples of intensive trenching studies, one on the Itoshizu-Tectonic Line in central Japan, and the other on the Miura Peninsula south of Tokyo, are briefly discussed with special reference to fault segmentation and the probability of large earthquakes. Studies of coastal morphology and deposits which are used for the reconstruction of paleoearthquakes are also reviewed. Japanese scientists have contributed much to paleoseismological studies overseas through collaborative international projects including identification of coseismic uplift, subsidence and tsunami deposits along the Pacific coasts as well as studies of inland faults.

Prediction probabilities from foreshocks

When any earthquake occurs, the possibility that it might be a foreshock increases the probability that a larger earthquake will occur nearby within the next few days. Clearly, the probability of a very large earthquake ought to be higher if the candidate foreshock were on or near a fault capable of producing that very large mainshock, especially if the fault is towards the end of its seismic cycle. We derive an expression for the probability of a major earthquake characteristic to a particular fault segment, given the occurrence of a potential foreshock near the fault. To evaluate this expression, we need: (1) the rate of background seismic activity in the area, (2) the long‐term probability of a large earthquake on the fault, and (3) the rate at which foreshocks precede large earthquakes, as a function of time, magnitude, and spatial location. For this last function we assume the average properties of foreshocks to moderate earthquakes in California: (1) the rate of mainshock occurrence after foreshocks decays roughly as t−1, so that most foreshocks are within three days of their mainshock, (2) foreshocks and mainshocks occur within 10 km of each other, and (3) the fraction of mainshocks with foreshocks increases linearly as the magnitude threshold for foreshocks decreases, with 50% of the mainshocks having foreshocks with magnitudes within three units of the mainshock magnitude (within three days). We apply our results to the San Andreas, Hayward, San Jacinto, and Imperial faults, using the probabilities of large earthquakes from the report of the Working Group on California Earthquake Probabilities (1988). The magnitude of candidate event required to produce a 1% probability of a large earthquake on the San Andreas fault within three days ranges from a high of 5.3 for the segment in San Gorgonio Pass to a low of 3.6 for the Carrizo Plain.

“Probabilities of Large Earthquakes in the San Francisco Bay Region” and “Probabilities of Large Scale Earthquakes Occurring in California on the San Andreas Fault”

“Probabilities of Large Earthquakes in the San Francisco Bay Region” and “Probabilities of Large Scale Earthquakes Occurring in California on the San Andreas Fault”