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1.
Tokutaro Hatori 《GeoJournal》1996,38(3):313-319
The regional characteristics of tsunami magnitudes in the SE Asia region are discussed in relation to earthquake magnitudes during the period from 1960 to 1994. Tsunami magnitudes on the Imamura-Iida scale are investigated by the author's method (Hatori 1979, 1986) using the data of inundation heights near the source area and tide-gauge records observed in Japan. The magnitude values of the Taiwan tsunamis showed relatively to be small. On the contrary, the magnitudes of tsunamis in the vicinities of the Philippines and Indonesia exceed more than 1–2 grade (tsunami heights: 2–5 times) compared to earthquakes with similar size on the circum-Pacific zone. The relation between tsunami magnitude, m, and earthquake magnitude, M s, is expressed as m = 2.66 M s– 17.5 for these regions. For example, the magnitudes for the 1976 Mindanao tsunami (M s= 7.8, 3702 deaths) and the 1992 Flores tsunami (M s= 7.5, 1713 deaths) were determined to be m = 3 and m = 2.5, respectively. The focal depth of tsunamigenic earthquakes is shallower thand< 36 km, and the detectively of tsunamis is small for deep earthquakes being d > 40 km. For future tsunamis, it is indispensable to take precautions against shallow earthquakes having the magnitudes M s> 6.5.  相似文献   

2.
In the paper we report the state-of-the-art of seismicity study in the Baikal rift system and the general results obtained. At present, the regional earthquake catalog for fifty years of the permanent instrumental observations consists of over 185,000 events. The spatial distribution of the epicenters, which either gather along well-delineated belts or in discrete swarms is considered in detail for different areas of the rift system. At the same time, the hypocenters are poorly constrained making it difficult to identify the fault geometry. Clustered events like aftershock sequences or earthquake swarms are typical patterns in the region; moreover, aftershocks of M ⩾ 4.7 earthquakes make up a quarter of the whole catalog. The maximum magnitude of earthquakes recorded instrumentally is MLH7.6 for a strike-slip event in the NE part of the Baikal rift system and MLH6.8 for a normal fault earthquake in the central part of the rift system (Lake Baikal basin). Predominant movement type is normal faulting on NE striking faults with a left lateral strike-slip component on W–E planes. In conclusion, some shortcomings of the seismic network and data processing are pointed out.  相似文献   

3.
In this paper the features of seismic process in the southern depression of Lake Baikal are considered. By the data on focal mechanisms of the earthquakes of February 25, 1999 (M w = 6.0), and August 27, 2008 (M w = 6.3), as well as based on configuration of their aftershock fields, it is determined that foci of strong seismic events in southern Baikal are controlled by the greatest structural elements of sublatitudinal and submeridional strikes. It has been shown that a substantial role in the formation of focal zones is played by low-scale destruction of the Earth’s crust, revealed by geological-geophysical data and proved by clustering of seismic shocks. New data on the August 27, 2008, earthquake have proved the high level of seismic danger of this part of the Baikal Rift Zone and allowed us to determine generation conditions of strong earthquakes more precisely.  相似文献   

4.
We present the seismic energy, strain energy, frequency–magnitude relation (b-value) and decay rate of aftershocks (p-value) for the aftershock sequences of the Andaman–Sumatra earthquakes of December 26, 2004 (M w 9.3) and March 28, 2005 (M w 8.7). The energy released in aftershocks of 2004 and 2005 earthquake was 0.135 and 0.365% of the energy of the respective mainshocks, while the strain release in aftershocks was 39 and 71% for the two earthquakes, respectively. The b-value and p-value indicate normal value of about 1. All these parameters are in normal range and indicate normal stress patterns and mechanical properties of the medium. Only the strain release in aftershocks was considerable. The fourth largest earthquake in this region since 2004 occurred in September 2007 off the southern coast of Island of Sumatra, generating a relatively minor tsunami as indicated by sea level gauges. The maximum wave amplitude as registered by the Padang, tide gauge, north of the earthquake epicenter was about 60 cm. TUNAMI-N2 model was used to investigate ability of the model to capture the minor tsunami and its effect on the eastern Indian Coast. A close comparison of the observed and simulated tsunami generation, propagation and wave height at tide gauge locations showed that the model was able to capture the minor tsunami phases. The directivity map shows that the maximum tsunami energy was in the southwest direction from the strike of the fault. Since the path of the tsunami for Indian coastlines is oblique, there were no impacts along the Indian coastlines except near the coast of epicentral region.  相似文献   

5.
The characteristics of seismicity prior to the series of eight very strong earthquakes (M w = 7.0–9.0) in Northeast Japan are discussed. Ring seismicity structures that appeared prior to all eight events in two depth ranges of 0–33 and 34–70 km are identified. The epicenters of the main shocks were located near areas of crossing or touching of shallow and deep rings. It was shown that the sizes of shallow rings and threshold magnitudes corresponding to seismicity rings grow with the energy of the main shocks. It was noted that the prognosis with respect to the place and magnitude of the catastrophic earthquake on March 11, 2011, had been made before it based on the data obtained prior to July 1, 2009. Use of the new data obtained prior to March 10, 2011, enabled us to specify this prognosis significantly. We obtained correlation dependences of threshold magnitudes on the energy of the main shocks (with a high correlation coefficients). It was shown that the duration of the period for seismicity rings to emerge in the considered region nearly did not depend on magnitude. The nature of annular structures and the possibility of application of their parameters for prognosis of strong earthquakes were discussed.  相似文献   

6.
Morphostructural zoning (MSZ) scheme of the Himalayan arc region as obtained from a joint study of topographic, geological and tectonic maps as well as satellite imagery is analysed. Three types of morphostructures have been determined: territorial units (blocks of different ranks), linear zones limiting these blocks (lineaments) and intersections of the lineaments (knots). Comparison of MSZ scheme with the know seismicity indicates epicenters of strong earthquakes (M≥6·5) clustered around some of these knots. Pattern recognition method is used to determine seismically potential areas for the occurrence of recognition method is used to determine seismically potential, for the occurrence of strong earthquakes of magnitude ≥M 0. We have carried out two such studies for the Himalayan arc region, one forM 0=6·5 and the other forM 0=7·0. Out of a total number of 97 knots, 48 knots are found to be seismically potential for the occurrence of earthquake ofM≥6·5. The results of the study forM 0=6·5 were presented in the symposium on “Earthquake Prediction” held in Strasbourg, France, March 1991 (Gorshkovet al 1991). The epicenter of Uttarkashi earthquake of magnitude,M b=6·6 that occurred in the late hours of 19th October 1991 (UTC) lies in the vicinity of one such knot. The second study carried out subsequently shows that only 36, knots are potential for the occurrence of earthquakes ofM≥7·0, which include the knot, associated with theUttarkashi earthquake.  相似文献   

7.
To explore the local tsunami hazard from the Cascadia subduction zone we (1) evaluate geologically reasonable variability of the earthquake rupture process, (2) specify 25 deterministic earthquake sources, and (3) use resulting vertical coseismic deformations for simulation of tsunami inundation at Cannon Beach, Oregon. Maximum runup was 9–30 m (NAVD88) from earthquakes with slip of ~8–38 m and M w ~8.3–9.4. Minimum subduction zone slip consistent with three tsunami deposits was 14–15 m. By assigning variable weights to the source scenarios using a logic tree, we derived percentile inundation lines that express the confidence level (percentage) that a Cascadia tsunami will not exceed the line. Ninety-nine percent of Cascadia tsunami variation is covered by runup ≤30 m and 90% ≤16 m with a “preferred” (highest weight) value of ~10 m. A hypothetical maximum-considered distant tsunami had runup of ~11 m, while the historical maximum was ~6.5 m.  相似文献   

8.
Xu  Zhiguo  Sun  Lining  Rahman  Mohd Nashriq Abd  Liang  Shanshan  Shi  Jianyu  Li  Hongwei 《Natural Hazards》2022,111(3):2703-2719

A major left-lateral strike-slip Mw7.7 earthquake occurred in the vicinity of the Caribbean Sea on January 28, 2020. As a result, a small-scale tsunami was generated. The properties of the seismogenic source were described using observational data gathered for the earthquake and tsunami, as well as information on the regional tectonic setting. The tsunami was simulated with the COMCOT model and Okada’s dislocation model from finite fault solutions for MW7.7 Caribbean Sea earthquakes published by the United States Geological Survey. The simulation results were compared to tide gauge records to validate whether the seafloor’s vertical displacement generated by the strike-slip fault caused a small-scale tsunami. We conducted a spectral analysis of the tsunami to better understand the characteristics of tsunami records. The tsunami simulation results showed that the co-seismic vertical displacement caused by a strike-slip MW7.7 earthquake could have contributed to the small-scale tsunami, but the anomalously large high-frequency tsunami waves recorded by the George Town tide gauge 11 min after the earthquake were unrelated to the earthquake-generated tsunami. According to the spectrum analysis, the predominant period of noticeable high-frequency tsunami waves recorded by the George Town tide gauge occurred only two minutes after the earthquake. This indicates that the source of the small-scale tsunami was close to the George Town station and the possible tsunami source was 150 km away from George Town station. These facts suggest that a submarine landslide was caused by the strike-slip earthquake. The comprehensive analysis showed that the small-scale tsunami was not caused solely by co-seismic seafloor deformation from the strike-slip event but that an earthquake-triggered submarine landslide was the primary cause. Therefore, the combined impact of two sources led to the small-scale tsunami.

  相似文献   

9.
A regional time and magnitude predictable model has been applied to estimate the recurrence intervals for large earthquakes in the vicinity of 8 October 2005 Kashmir Himalaya earthquake (25°–40°N and 65°–85°E), which includes India, Pakistan, Afghanistan, Hindukush, Pamirs, Mangolia and Tien-Shan. This region has been divided into 17 seismogenic sources on the basis of certain seismotectonics and geomorphological criteria. A complete earthquake catalogue (historical and instrumental) of magnitude Ms ≥ 5.5 during the period 1853–2005 has been used in the analysis. According to this model, the magnitude of preceding earthquake governs the time of occurrence and magnitude of future mainshock in the sequence. The interevent time between successive mainshocks with magnitude equal to or greater than a minimum magnitude threshold were considered and used for long-term earthquake prediction in each of seismogenic sources. The interevent times and magnitudes of mainshocks have been used to determine the following predictive relations: logT t = 0.05 M min + 0.09 M p − 0.01 log M 0 + 01.14; and M f = 0.21 M min − 0.01 M p + 0.03 log M 0 + 7.21 where, T t is the interevent time of successive mainshocks, M min is minimum magnitude threshold considered, M p is magnitude of preceding mainshock, M f is magnitude of following mainshock and M 0 is the seismic moment released per year in each seismogenic source. It was found that the magnitude of following mainshock (M f) does not depend on the interevent time (T t), which indicates the ability to predict the time of occurrence of future mainshock. A negative correlation between magnitude of following mainshock (M f) and preceding mainshock (M p) indicates that the larger earthquake is followed by smaller one and vice versa. The above equations have been used for the seismic hazard assessment in the considered region. Based on the model applicability in the studied region and taking into account the occurrence time and magnitude of last mainshock in each seismogenic source, the time-dependent conditional probabilities (PC) for the occurrence of next shallow large mainshocks (Ms ≥ 6.5), during next 20 years as well as the expected magnitudes have been estimated.  相似文献   

10.
The status of Reservoir Induced Seismicity (RIS) has been reviewed periodically (Rothé, 1968, 1973; Gupta and Rastogi, 1976; Simpson, 1976; Packer et al., 1979). In the present paper, the significant work carried out during the last three years on RIS is reviewed.An earthquake of magnitude occurred on November 14, 1981 in the vicinity of Aswan Lake, Egypt, 17 years after the filling started in 1964. This event occurred 4 days after the seasonal maximum in the reservoir water level and was followed by a long sequence of aftershocks. Another event of magnitude occurred in the vicinity of Aswan Lake on August 20, 1982. Results of preliminary investigations indicate that this seismic activity is reservoir induced. Recent analyses of induced seismic events at Nurek Reservoir U.S.S.R., show that the second stage of filling during August to December 1976, increasing the maximum depth from 120 m to 200 m, was accompanied by an intense burst of shallow seismic activity. An outward migration from the centre of the reservoir, possibly associated with diffusion of pore pressure, is revealed by the temporal distribution of earthquake foci. A variety of investigations including the in situ measurement of tectonic stress, pore pressure, permeability, distribution of faults, etc., in addition to monitoring seismicity, have been undertaken in the vicinity of the Monticello Reservoir, South Carolina. The largest reservoir induced earthquake is predicted not to exceed magnitude 5.The Koyna Reservoir, India, continues to be the most outstanding example of RIS. Three earthquakes of magnitude 5 occurred in September 1980. Earthquakes of magnitude 4 occur frequently in the vicinity of Koyna, the latest being on February 5, 1983. Events that occurred during the period 1967–1973 have been relocated using better procedures and are found to be much shallower and the epicentres less diffused. Location of 12 earthquakes of Ms 4.0, their foreshocks and aftershocks, that occurred during 1973–1976, composite focal mechanism solutions and related studies are consistent with the delineation of a N-S trending fault through the reservoir area. In a couple of interesting studies it has been demonstrated that earthquakes of magnitude 5.0 in the Koyna region are usually preceded by several magnitude 4 earthquakes in the preceding fortnight. Also, a rate of loading of Koyna reservoir of at least 40 ft/week appears to be a necessary, although not sufficient, condition for the occurrence of magnitude 5 earthquakes. Smooth filling/emptying appears to be the key to reduce the hazard of RIS.A map and a table of the reported cases of reservoir induced changes in seismicity through 1982 have been compiled.  相似文献   

11.
The return periods and occurrence probabilities related to medium and large earthquakes (M w 4.0–7.0) in four seismic zones in northeast India and adjoining region (20°–32°N and 87°–100°E) have been estimated with the help of well-known extreme value theory using three methods given by Gumbel (1958), Knopoff and Kagan (1977) and Bury (1999). In the present analysis, the return periods, the most probable maximum magnitude in a specified time period and probabilities of occurrences of earthquakes of magnitude M ≥ 4.0 have been computed using a homogeneous and complete earthquake catalogue prepared for the period between 1897 and 2007. The analysis indicates that the most probable largest annual earthquakes are close to 4.6, 5.1, 5.2, 5.5 and 5.8 in the four seismic zones, namely, the Shillong Plateau Zone, the Eastern Syntaxis Zone, the Himalayan Thrusts Zone, the Arakan-Yoma subduction zone and the whole region, respectively. The most probable largest earthquakes that may occur within different time periods have been also estimated and reported. The study reveals that the estimated mean return periods for the earthquake of magnitude M w 6.5 are about 6–7 years, 9–10 years, 59–78 years, 72–115 years and 88–127 years in the whole region, the Arakan-Yoma subduction zone, the Himalayan Thrusts Zone, the Shillong Plateau Zone and the Eastern Syntaxis Zone, respectively. The study indicates that Arakan-Yoma subduction zone has the lowest mean return periods and high occurrence probability for the same earthquake magnitude in comparison to the other zones. The differences in the hazard parameters from zone to zone reveal the high crustal heterogeneity and seismotectonics complexity in northeast India and adjoining regions.  相似文献   

12.
Öncel  A. O.  Alptekin  Ö. 《Natural Hazards》1999,19(1):1-11
In order to investigate the effect of aftershocks on earthquake hazard estimation, earthquake hazard parameters (m, b and Mmax) have been estimated by the maximum likelihood method from the main shocks catalogue and the raw earthquakes catalogue for the North Anatolian Fault Zone (NAFZ). The main shocks catalogue has been compiled from the raw earthquake catalogue by eliminating the aftershocks using the window method. The raw earthquake catalogue consisted of instrumentally detected earthquakes between 1900 and 1992, and historical earthquakes that occurred between 1000–1900. For the events of the mainshock catalogue the Poisson process is valid and for the raw earthquake catalogue it does not fit. The paper demonstrates differences in the hazard outputs if on one hand the main catalogues and on the other hand the raw catalogue is used. The maximum likelihood method which allows the use of the mixed earthquake catalogue containing incomplete (historical) and complete (instrumental) earthquake data is used to determine the earthquake hazard parameters. The maximum regional magnitude (Mmax, the seismic activity rate (m), the mean return period (R) and the b value of the magnitude-frequency relation have been estimated for the 24°–31° E, 31°–41° E, 41°–45° E sections of the North Anatolian Fault Zone from the raw earthquake catalogue and the main shocks catalogue. Our results indicate that inclusion of aftershocks changes the b value and the seismic activity rate m depending on the proportion of aftershocks in a region while it does not significantly effect the value of the maximum regional magnitude since it is related to the maximum observed magnitude. These changes in the earthquake hazard parameters caused the return periods to be over- and underestimated for smaller and larger events, respectively.  相似文献   

13.
During two distinct earthquakes occurred on March 7, 1867 and October 6, 1944, tsunami waves were also observed at some localities around the Gulf of Edremit, NE Aegean Sea. The first event (M w = 6.8) mostly affected the city of Mitilini of Lesvos Island while the Gulf of Edremit-Ayvacık earthquake (M S = 6.8) largely affected the northern and eastern coastal areas of the Gulf of Edremit. In 1944 earthquake, numerous surface cracks and water gushes were reported. The coastal neighborhoods of the town of Ayvalık in the east were flooded by tsunami waves. At the WSW extend of the main fault observed on land, which is parallel to the present-day slip vectors, some normal-oblique faults were observed close and subparallel to the northern coast. On the basis of historical documents, reports, interviews, geological setting, field observations and marine seismic reflection data, the 1944 earthquake was not triggered by one of the main fault segments but by a secondary fault or fault group which was described in this study. Depending on the distribution of tensional and compressional forces in the region, which rotates clockwise under the control of the middle strand of the North Anatolian fault, secondary fault groups become important. The moment tensor parameters of such small-size events have been determined and have obtained consistent results with the faults proposed in this study.  相似文献   

14.
The maximum magnitude, the activity rate, and the Gutenberg-Richterb parameter as earthquake hazard parameters, have been evaluated for Sweden. The maximum likelihood method permits the combination of historical and instrumental data. The catalog used consists of 1100 earthquakes in the time interval 1375–1989. The extreme part of the catalog contains only the strongest historical earthquakes, whereas the complete part is divided into several subcatalogs, each assumed complete above a specified threshold magnitude. The uncertainty in magnitude determination was taken into account. For southern Sweden, the calculations giveb-values of 1.04 (0.05) for the whole area south of 60° N and 0.98 (0.06) for a subregion of enhanced seismicity in the Lake Vänern area. For the whole area north of 60° N, theb-value is 1.35 (0.06) and for the seismicity zone along the Gulf of Bothnia 1.26 (0.06). The number of annually expected earthquakes with magnitude equal to or larger than 2.4 [ML(UPP) or MM(UPP)] is 1.8 for the whole southern Sweden, 1.3 for the Lake Vänern region, 3.7 for northern Sweden, and 2.4 for the region along the Gulf of Bothnia. The maximum expected regional magnitude is calculated to 4.9 (0.5) for a time span of 615 years for southern Sweden and the Lake Vänern subregion, and 4.3 (0.5) for a time span of 331 years for northern Sweden and the Gulf of Bothnia subregion. However, several historical earthquakes with magnitude above 5 in nearby areas of Norway indicate that the seismic potential may be higher.  相似文献   

15.
Abstract: There were huge life and property losses during the Ms8.0 Wenchuan earthquake on May 12, 2008. Strain fluctuation curves were completely recorded at stress observatory stations in the Qinghai-Tibet plateau and its surroundings in the process of the earthquake. This paper introduces the geological background of the Wenchuan earthquake and the profile of in-situ stress monitoring stations. In particular, data of 174 earthquakes (Ms4.0-Ms8.5) were processed and analyzed with various methods, which were recorded at the Shandan station from August 2007 to December 2008. The results were compared with other seismic data, and further analyses were done for the recoded strain seismic waves, co-seismic strain stepovers, pre-earthquake strain valleys, Earth’s free oscillations before and after the earthquake and their physical implications. During the Wenchuan earthquake, the strainmeter recorded a huge extensional strain of 70 seconds, which shows that the Wenchuan earthquake is a rupture process predominated by thrusting. Significant precursory strain anomalies were detected 48 hours, 30 hours, 8 hours and 37 minutes before the earthquake. The anomalies are very high and their forms are very similar to that of the main shock. Similar anomalies can also be found in strain curves of other shocks greater than Ms7.0, indicating that such anomalies are prevalent before a great earthquake. In this paper, it is shown that medium aftershocks (Ms5.5-6.0) can also cause Earth’s free oscillations. Study of free oscillations is of great significance to understand the internal structure of the Earth and focal mechanisms of earthquakes and to recognize slow shocks, thus providing a scientific basis for the prevention and treatment of geological disasters and the prediction of future earthquakes.  相似文献   

16.
The mechanics of the ice cover of Lake Baikal has been studied through monitoring of its deformation and seismic effects and full-sizeuniaxial compression and shear tests in 2005–2007. We measured the shear strength of ice specimens and large in situ blocks (σ = 0.2?1.9 MPa) and investigated it as a function of air temperature and ice structure. Deformation was analyzed in terms of various natural controls, such as air temperature and pressure, wind, sub-ice currents, and local earthquakes. Precise strain measurements along ice cracks were used to explore the strain behavior of ice, including the cases of dynamic failure (ice shocks). Measurements by seismic station Baikal-12 were used to monitor diurnal background micro seismicity variations and to record an ice quake with its magnitude (M = 0.3–0.8; E = 104–105 J) comparable to a medium-size rock burst or a small earthquake. Ice quakes were studied in terms of their nucleation, dynamics, and after effects, as well as the strain and seismic responses of the ice, using sub-ice explosions in the latter case. The natural conditions of deformation in the elastoviscoplastic Baikal ice are similar to lithospheric processes and thus can be employed in tectonophysical modeling with scientific and practical implications for hazard mitigation.  相似文献   

17.
The Vienna Basin Transfer Fault (VBTF) is a slow active fault with moderate seismicity (I max~8–9, M max~5.7) passing through the most vulnerable regions of Austria and Slovakia. We use different data to constrain the seismic potential of the VBTF including slip values computed from the seismic energy release during the 20th century, geological data on fault segmentation and a depth-extrapolated 3-D model of a generalized fault surface, which is used to define potential rupture zones. The seismic slip of the VBTF as a whole is in the range of 0.22–0.31 mm/year for a seismogenic fault thickness of 8 km. Seismic slip rates for individual segments vary from 0.00 to 0.77 mm/year. Comparing these data to geologically and GPS-derived slip velocities (>1 mm/year) proofs that the fault yields a significant seismic slip deficit. Segments of the fault with high seismic slip contrast from segments with no slip representing locked segments. Fault surfaces of segments within the seismogenic zone (4–14 km depth) vary from 55 to 400 km2. Empirical scaling relations show that these segments are sufficiently large to explain both, earthquakes observed in the last centuries, and the 4th century Carnuntum earthquake, for which archeo-seismological data suggest a magnitude of M ≥ 6. Based on the combination of all data (incomplete earthquake catalog, seismic slip deficits, locked segments, potential rupture areas, indications of strong pre-catalog earthquakes) we argue, that the maximum credible earthquake for the VBTF is in the range M max = 6.0–6.8, significantly larger than the magnitude of the strongest recorded events (M = 5.7).  相似文献   

18.
The Algerian margin is a seismically active region, where during the last century, several large magnitude earthquakes took place. This study combines geotechnical and sedimentological data with numerical modelling to quantitatively assess the present-day slope stability of the Algerian margin. Geotechnical laboratory tests, such as cyclic triaxial tests, oedometric tests and vane shear tests were carried out on sediment cores collected on the study area. The liquefaction potential of a sediment column located about 30 km from the Boumerdès earthquake epicentre of 21st May 2003 was evaluated theoretically for an earthquake of M w  = 6.8. We show that thin sand and silt beds such as those described on recovered sediment cores are the main cause of sediment deformation and liquefaction during earthquakes. Numerical calculations showed that the slope failure may occur during an earthquake characterised by a PGA in excess of 0.1g, and also that, under a PGA of 0.2g liquefaction could be triggered in shallow silty–sandy deposits. Moreover, comparison of the predicted slope failure with failure geometries inferred from seafloor morphology showed that earthquakes and subsequent mass movements could explain the present-day morphology of the study area.  相似文献   

19.
North-east India is seismically very active and has experienced many widelydistributed shallow, large earthquakes. Earthquake generation model for the region was studied using seismicity data [(1906–1984) prepared by National Geophysical Data Centre (NGDC), Boulder Colorado, USA]. For establishing statistical relations surface wave magnitudes (M s≥5·5) have been considered. In the region four seismogenic sources have been identified which show the occurrences of atleast three earthquakes of magnitude 5·5≤M s≤7·5 giving two repeat times. It is observed that the time interval between the two consecutive main shock depends on the preceding main shock magnitude (M p) and not on the following main shock magnitude (M f) revealing the validity of time predictable model for the region. Linear relation between logarithm of repeat time (T) and preceding main shock magnitude (M p) is established in the form of logT=cM p+a. The values ofc anda are estimated to be 0–36 and 1–23, respectively. The relation may be used for seismic hazard evaluation in the region.  相似文献   

20.
We investigate the time dependence of the number of deaths reported through Internet after earthquakes and/or earthquake-generated tsunami. An approximate relation N(t) = N 0 [1 − exp(−αt)] is used to describe such temporal variation, in which N(t) is the number of deaths reported at time t, N 0 is the final number of deaths, and α is the coefficient reflecting the rescue process. We considered 12 earthquake cases since 2001 using the information from the web, which shows that the N-t relation approximates the data, and the logarithm of α is reversely proportional to the magnitude of earthquake, albeit with significant uncertainties. Quick and rough estimate of the final death toll can be made using this simple and approximate relation, with the empirical α-M relation as a reference. For the 12 cases under consideration, quick and rough estimate of fatalities can be obtained 2 days after the earthquake, fitting the real situation in the order of magnitudes. Although being very rough, this estimate can assist the emergency decision-making and can be revised as time lapses. When more and more data becomes available, curve fitting can provide both N 0 and α at the same time. The method is tested against the data of the recent Yushu earthquake on April 14, 2010.  相似文献   

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