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1.
The Pattern Informatics (PI) technique [Tiampo, K.F., Rundle, J.B., McGinnis, S., Gross, S., Klein, W., 2002. Mean-field threshold systems and phase dynamics: An application to earthquake fault systems, Europhys. Lett., 60, 481–487] is founded on the premise that changes in the seismicity rate are a proxy for changes in the underlying stress. This new approach to the study of seismicity quantifies its local and regional space–time patterns and identifies regions of local quiescence or activation. Here we use a modification of the PI method to quantify localized changes surrounding the epicenters of large earthquakes in California in an attempt to objectively quantify the rupture zones of these upcoming events. We show that this method can be used to forecast the size and magnitude of future earthquakes.  相似文献   

2.
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3.
Yosihiko Ogata   《Tectonophysics》2006,424(3-4):291
This paper is concerned with the intermediate-term prediction of the forthcoming M7.4–8.2 earthquake on the plate boundary, off the east coast of Miyagi Prefecture, northern Japan, which has the highest occurrence probability among the long-term forecasted events announced to the public. Seismicity and aftershocks in the regions of stress-shadow preceding each of the previous ruptures in 1936 and 1978 shows significantly lower activity than the predicted rate by the ETAS model (the relative quiescence) during some years preceding the events, whereas the seismicity is normal or even activated in the regions of neutral or increasing Coulomb failure stress (CFS), which leads to the scenario based on the likely precursory slip within or near the source. Assuming such a scenario, a number of sequences of earthquakes or aftershocks during 1979–2004 from various regions in northern Japan are selected to analyze them by fitting the ETAS model. Then the results are examined in relation to the CFS increments in the considered regions using the source models of the 1793, 1936 and 1978 interplate ruptures, and additionally the source model of recently occurred 2003 Miyagi-Ken-Oki intra-slab earthquake of M7.1. It is likely that the results of the normal activity and relative quiescence in the respective activities are due to the preslip of the intra-slab earthquake rather than the preslip of the expected rupture on the plate boundary.  相似文献   

4.
The Japan Trench subduction zone, located east of NE Japan, has regional variation in seismicity. Many large earthquakes occurred in the northern part of Japan Trench, but few in the southern part. Off Miyagi region is in the middle of the Japan Trench, where the large earthquakes (M > 7) with thrust mechanisms have occurred at an interval of about 40 years in two parts: inner trench slope and near land. A seismic experiment using 36 ocean bottom seismographs (OBS) and a 12,000 cu. in. airgun array was conducted to determine a detailed, 2D velocity structure in the forearc region off Miyagi. The depth to the Moho is 21 km, at 115 km from the trench axis, and becomes progressively deeper landward. The P-wave velocity of the mantle wedge is 7.9–8.1 km/s, which is typical velocity for uppermost mantle without large serpentinization. The dip angle of oceanic crust is increased from 5–6° near the trench axis to 23° 150 km landward from the trench axis. The P-wave velocity of the oceanic uppermost mantle is as small as 7.7 km/s. This low-velocity oceanic mantle seems to be caused by not a lateral anisotropy but some subduction process. By comparison with the seismicity off Miyagi, the subduction zone can be divided into four parts: 1) Seaward of the trench axis, the seismicity is low and normal fault-type earthquakes occur associated with the destruction of oceanic lithosphere. 2) Beneath the deformed zone landward of the trench axis, the plate boundary is characterized as a stable sliding fault plain. In case of earthquakes, this zone may be tsunamigenic. 3) Below forearc crust where P-wave velocity is almost 6 km/s and larger: this zone is the seismogenic zone below inner trench slope, which is a plate boundary between the forearc and oceanic crusts. 4) Below mantle wedge: the rupture zones of thrust large earthquakes near land (e.g. 1978 off Miyagi earthquake) are located beneath the mantle wedge. The depth of the rupture zones is 30–50 km below sea level. From the comparison, the rupture zones of large earthquakes off Miyagi are limited in two parts: plate boundary between the forearc and oceanic crusts and below mantle wedge. This limitation is a rare case for subduction zone. Although the seismogenic process beneath the mantle wedge is not fully clarified, our observation suggests the two possibilities: earthquake generation at the plate boundary overridden by the mantle wedge without serpentinization or that in the subducting slab.  相似文献   

5.
Short term spatial and temporal variations in seismicity prior to the three sequences of earthquakes of mb 5.8 of the Burma—Szechwan region are studied. Six years (1971–1976) of ISC seismicity data, as reported in the Regional Catalogue of Earthquakes, are considered. During the period, six earthquakes of body wave magnitude mb 5.8 occurred in four sequences. Of these, three sequences are preceded by swarm activity in the epicentral regions. Evison (1977b) suggested that the swarm before the sequences of large shocks is a possible long-term precursor. He derived the conclusion by analyzing earthquakes in New Zealand and California. The analysis of the seismicity data for the region under investigation supports Evison's view and suggests that a relation between swarms and sequences of large events exists. The precursory time period (i.e. the time from beginning of the swarm to the main shock) for the Szechwan earthquakes of mb = 5.9 (Feb. 6, 1973) and mb = 5.8 (May 10, 1974) and the Burma earthquake of mb = 6.2 (Aug. 12, 1976) are 305, 317 and 440 days, respectively.  相似文献   

6.
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7.
The Load/Unload Response Ratio (LURR) method is proposed for short-to-intermediate-term earthquake prediction [Yin, X.C., Chen, X.Z., Song, Z.P., Yin, C., 1995. A New Approach to Earthquake Prediction — The Load/Unload Response Ratio (LURR) Theory, Pure Appl. Geophys., 145, 701–715]. This method is based on measuring the ratio between Benioff strains released during the time periods of loading and unloading, corresponding to the Coulomb Failure Stress change induced by Earth tides on optimally oriented faults. According to the method, the LURR time series usually climb to an anomalously high peak prior to occurrence of a large earthquake. Previous studies have indicated that the size of critical seismogenic region selected for LURR measurements has great influence on the evaluation of LURR. In this study, we replace the circular region usually adopted in LURR practice with an area within which the tectonic stress change would mostly affect the Coulomb stress on a potential seismogenic fault of a future event. The Coulomb stress change before a hypothetical earthquake is calculated based on a simple back-slip dislocation model of the event. This new algorithm, by combining the LURR method with our choice of identified area with increased Coulomb stress, is devised to improve the sensitivity of LURR to measure criticality of stress accumulation before a large earthquake. Retrospective tests of this algorithm on four large earthquakes occurred in California over the last two decades show remarkable enhancement of the LURR precursory anomalies. For some strong events of lesser magnitudes occurred in the same neighborhoods and during the same time periods, significant anomalies are found if circular areas are used, and are not found if increased Coulomb stress areas are used for LURR data selection. The unique feature of this algorithm may provide stronger constraints on forecasts of the size and location of future large events.  相似文献   

8.
In this study, we analyze the recent (1990–1997) seismicity that affected the northern sector (Sannio–Benevento area) of the Southern Apennines chain. We applied the Best Estimate Method (BEM), which collapses hypocentral clouds, to the events of low energy (Md max=4.1) seismic sequences in order to constrain the location and geometry of the seismogenetic structures. The results indicate that earthquakes aligned along three main structures: two sub-parallel structures striking NW–SE (1990–1992, Benevento sequence) and one structure striking NE–SW (1997, Sannio sequence). The southernmost NW–SE structure, which dips towards NE, overlies the fault that is likely to be responsible for a larger historical earthquake (Io max=XI MCS, 1688 earthquake). The northernmost NW–SE striking structure dips towards SW. The NE–SW striking structure is sub-vertical and it is located at the northern tip of the fault segment supposed to be responsible for the 1688 earthquake. The spatio-temporal evolution of the 1990–1997 seismicity indicates a progressive migration from SE (Benevento) to NW (Sannio) associated to a deepening of hypocenters (i.e., from about 5 to 12 km). Hypocenters cluster at the interface between the major structural discontinuities (e.g., pre-existing thrust surfaces) or within higher rigidity layers (e.g., the Apulia carbonates). Available focal mechanisms from earthquakes occurred on the recognized NW–SE and NE–SW faults are consistent with dip-slip normal solutions. This evidences the occurrence of coexisting NW–SE and NE–SW extensions in Southern Apennines.  相似文献   

9.
According to previous observations [Geophys. Res. Lett. 27 (2000) 3957], the generation of large (M≥7.0) earthquakes in the western part of the north Anatolian fault system (Marmara Sea) is followed by strong earthquakes along the Northern Boundary of the Aegean microplate (NAB: northwestermost Anatolia–northern Aegean–central Greece–Ionian islands). Therefore, it can be hypothesized that a seismic excitation along this boundary should be expected after the occurrence of the Izmit 1999 earthquake (M=7.6). We have applied the method of accelerating seismic crustal deformation, which is based on concepts of critical point dynamics in an attempt to locate more precisely those regions along the NAB where seismic excitation is more likely to occur. For this reason, a detailed parametric grid search of the broader NAB area was performed for the identification of accelerating energy release behavior.Three such elliptical critical regions have been identified with centers along this boundary. The first region, (A), is centered in the eastern part of this boundary (40.2°N, 27.2°E: southwest of Marmara), the second region, (B), has a center in the middle part of the boundary (38.8°N, 23.4°E: East Central Greece) and the third region, (C), in the westernmost part of the boundary (38.2°N, 20.9°E: Ionian Islands). The study of the time variation of the cumulative Benioff strain in two of the three identified regions (A and B) revealed that intense accelerating seismicity is observed especially after the occurrence of the 1999 Izmit mainshock. Therefore, it can be suggested that the seismic excitation, at least in these two regions, has been triggered by the Izmit mainshock.Estimations of the magnitudes and origin times of the expected mainshocks in these three critical regions have also been performed, assuming that the accelerating seismicity in these regions will lead to a critical point, that is, to the generation of mainshocks.  相似文献   

10.
The Chi-Chi 1999 earthquake ruptured the out-of-sequence Chelungpu Thrust Fault (CTF) in the fold-and-thrust belt in Western Central Taiwan. An important feature of this rupture is that the calculated slip increases approximately linearly in the SE–NW convergence plate direction from very little at its deeper edge to a maximum near the surface. We propose here a new explanation for this co-seismic slip distribution based on the study of both stress and displacement over the long-term as well as over a seismic cycle. Over the last 0.5 My, the convergence rate in the mountain front belt is accommodated by the frontal Changhua Fault (Ch.F), the CTF and the Shuangtung Fault (Sh.F). Based on previously published balanced cross sections, we estimate that the long-term slip of the Ch.F and of the CTF accommodate 5–30% and 30–55% of the convergence rate, respectively. This long-term partitioning of the convergence rate and the modeling of inter-seismic and post-seismic displacements suggest that the peculiar linear co-seismic slip distribution is accounted for by a combination of the effect of the obliquity of the CTF to the direction of inter-seismic loading, and of increasing aseismic creep on the deeper part of the Ch.F and CTF. Many previous interpretations of this slip distribution have been done including the effects of material properties, lubrication, site effect, fault geometry and dynamic waves. The importance of these processes with respect to the effects proposed here is still unknown. Taking into account the dip angle of the CTF, asperity dynamic models have been proposed to explain the general features of co-seismic slip distribution. In particular, recent works show the importance of heterogeneous spatial distribution of stress prior to the Chi-Chi earthquake. Our analysis of seismicity shows that previous large historic earthquakes cannot explain the amplitude of this heterogeneity. Based on our approach, we rather think that the high stress in the northern part of the CTF proposed by Oglesby and Day [Oglesby, D.D., Day, S.M., 2001. Fault geometry and the dynamics of the 1999 Chi-Chi (Taiwan) earthquake. Bull. Seismol. Soc. Am. 91, 1099–1111] reflects the latitudinal variation of inter-seismic coupling due to the obliquity of the CTF.  相似文献   

11.
Recent reliable data are used to study the behavior of seismic activity before 46 strong shallow earthquakes (M ≥ 6.0), which correspond to five complete samples of mainshocks. These samples include 6 mainshocks (M = 6.0–7.1) that occurred in western Mediterranean since 1980, 17 mainshocks (M = 6.0–7.2) which occurred in the Aegean (Greece and surrounding area) since 1980, 5 mainshocks (M = 6.4–7.5) that occurred in Anatolia since 1980, 12 mainshocks (M = 6.0–7.3) that occurred in California since 1980 and 6 mainshocks (M = 7.0–8.3) that occurred in Japan since 1990. In all 46 cases, a similar precursory seismicity pattern is observed. Specifically, it is observed that accelerating Benioff strain (square root of seismic energy) release caused by preshocks occurs in a broad circular region (critical region), with a radius about eight times larger than the fault length of the mainshock, in agreement with results obtained by various research groups during the last two decades. However, in a much smaller circular region (seismogenic region), with a radius about four times the fault length, the corresponding preshock strain decelerates with the time to the mainshock. The time variation of the strain follows in both cases a power law but the exponent power is smaller than unit (m ¯ = 0.3) in the case of the accelerating preshock strain and larger than unit (m ¯ = 3.0) in the case of the decelerating preshock strain. Predictive properties of this “Decelerating In–Accelerating Out Strain” model are expressed by empirical relations. The possibility of using this model for intermediate-term earthquake prediction is discussed and the relative model uncertainties are estimated.  相似文献   

12.
This study analyzed the rupture directivity of the 2011 Tohoku earthquake by using 100-s Rayleigh-wave travel-times, influenced by the finite source, to derive the fault parameters of the earthquake. The results demonstrated that the earthquake exhibited a slow rupture propagation with a rupture velocity of approximately 1.5–2.0 km/s and asymmetric bilateral faulting. The two rupture directions were N60°E and N127°E, with rupture lengths of approximately 276 km and 231 km, respectively. The rupture toward N60°E had a source duration of approximately 183 s, longer than that toward N127°E (approximately 156 s). Overall, the entire source duration of the earthquake faulting lasted approximately 183 s. Regarding historical seismicity in eastern Japan, the 2011 Tohoku earthquake not only ruptured a locked area in which large earthquakes have rarely occurred, but also ruptured the source regions of several historical earthquakes. With the exception of its slow rupture velocity and generation of a tsunami, the rupture features of the 2011 Tohoku earthquake were inconsistent with those of typical tsunami earthquakes.  相似文献   

13.
Yong—gangLI 《地学前缘》2003,10(4):479-505
美国加利福尼亚州兰德斯和海克特曼恩地区于1992年和1999年先后发生7.4级和7.1级地震,分别在地面产生80km和40km长的断裂带。震后在断裂带布置的密集地震站台记录到明显的断层导波(fault-zone guided waves)。这些导波由断层带内的余震和人工震源激发产生,走时在S波之后,但具有比体波更强的振幅和更长的波列,并具有频散特征。通过对2～7 Hz断层导波的定量分析和三维有限差分数字模拟,获得了震深区断裂带的高分辨内部构造图像以及岩石的物理特性。数字模拟结果表明这些断裂带上存在被严重破碎了的核心层,形成低速、低Q值地震波导。核心破碎带宽约100～200 m,其内地震波波速降为周围岩石的40％～50％,Q值约为10～50。根据岩石断裂力学观点,这一低速、低Q值带可被解释为地震过程中处于断层动态断裂前端的非弹性区(或称之为破碎区,相干过程区)。在兰德斯和海克特曼恩断裂带测得的破碎区宽度与断裂带长度之比约为0.005,基本上符合岩石断裂力学预期的结果。观察到的断层导波还显示兰德斯和海克特曼恩地震中多条断层发生滑移和破碎。兰德斯地震时多条阶梯形断层相继断裂;而在海克特曼恩地震中,断裂带南北两端均出现分枝断裂,深处的分枝断裂较地表出现的破裂状况更为复杂。由三维有限元模拟的动态断裂过程表明,?  相似文献   

14.
Active faulting and seismic properties are re-investigated in the eastern precinct of the city of Thessaloniki (Northern Greece), which was seriously affected by two large earthquakes during the 20th century and severe damage was done by the 1759 event. It is suggested that the earthquake fault associated with the occurrence of the latest destructive 1978 Thessaloniki earthquake continues westwards to the 20-km-long Thessaloniki–Gerakarou Fault Zone (TGFZ), which extends from the Gerakarou village to the city of Thessaloniki. This fault zone exhibits a constant dip to the N and is characterised by a complicated geometry comprised of inherited 100°-trending faults that form multi-level branching (tree-like fault geometry) along with NNE- to NE-trending faults. The TGFZ is compatible with the contemporary regional N–S extensional stress field that tends to modify the pre-existing NW–SE tectonic fabric prevailing in the mountainous region of Thessaloniki. Both the 1978 earthquake fault and TGFZ belong to a ca. 65-km-long E–W-trending rupture fault system that runs through the southern part of the Mygdonia graben from the Strymonikos gulf to Thessaloniki. This fault system, here called Thessaloniki–Rentina Fault System (TRFS), consists of two 17–20-km-long left-stepping 100°-trending main fault strands that form underlapping steps bridged by 8–10-km-long ENE–WSW faults. The occurrence of large (M6.0) historical earthquakes (in 620, 677 and 700 A.D.) demonstrates repeated activation, and therefore the possible reactivation of the westernmost segment, the TGFZ, could be a major threat to the city of Thessaloniki. Changes in the Coulomb failure function (ΔCFF) due to the occurrence of the 1978 earthquake calculated out in this paper indicate that the TGFZ has been brought closer to failure, a convincing argument for future seismic hazard along the TGFZ.  相似文献   

15.
Worldwide analysis of the clustering of earthquakes has lead to the hypothesis that the occurrence of abnormally large clusters indicates an increase in probability of a strong earthquake in the next 3–4 years within the same region. Three long-term premonitory seismicity patterns, which correspond to different non-contradictory definitions of abnormally large clusters, were tested retrospectively in 15 regions. The results of the tests suggest that about 80% of the strongest earthquakes can be predicted by monitoring these patterns.Most of results concern pattern B (“burst of aftershocks”) i.e. an earthquake of medium magnitude with an abnormally large number of aftershocks during the first few days. Two other patterns, S and Σ often complement pattern B and can replace it in some regions where the catalogs show very few aftershocks.The practical application of these patterns is strongly limited by the fact that neither the location of the coming earthquake within the region nor its time of occurrence within 3–4 years is indicated. However, these patterns present the possibility of increasing the reliability of medium and short-term precursors; also, they allow activation of some important early preparatory measures.The results impose the following empirical constraint on the theory of the generation of a strong earthquake: it is preceded by abnormal clustering of weaker earthquakes in the space-time-energy domain; corresponding clusters are few but may occur in a wide region around the location of the coming strong earthquake; the distances are of the same order as for the other reported precursors.  相似文献   

16.
The Himalayas has experienced varying rates of earthquake occurrence in the past in its seismo-tectonically distinguished segments which may be attributed to different physical processes of accumulation of stress and its release, and due diligence is required for its inclusion for working out the seismic hazard. The present paper intends to revisit the various earthquake occurrence models applied to Himalayas and examines it in the light of recent damaging earthquakes in Himalayan belt. Due to discordant seismicity of Himalayas, three types of regions have been considered to estimate larger return period events. The regions selected are (1) the North-West Himalayan Fold and Thrust Belt which is seismically very active, (2) the Garhwal Himalaya which has never experienced large earthquake although sufficient stress exists and (3) the Nepal region which is very seismically active region due to unlocked rupture and frequently experienced large earthquake events. The seismicity parameters have been revisited using two earthquake recurrence models namely constant seismicity and constant moment release. For constant moment release model, the strain rates have been derived from global strain rate model and are converted into seismic moment of earthquake events considering the geometry of the finite source and the rates being consumed fully by the contemporary seismicity. Probability of earthquake occurrence with time has been estimated for each region using both models and compared assuming Poissonian distribution. The results show that seismicity for North-West region is observed to be relatively less when estimated using constant seismicity model which implies that either the occupied accumulated stress is not being unconfined in the form of earthquakes or the compiled earthquake catalogue is insufficient. Similar trend has been observed for seismic gap area but with lesser difference reported from both methods. However, for the Nepal region, the estimated seismicity by the two methods has been found to be relatively less when estimated using constant moment release model which implies that in the Nepal region, accumulated strain is releasing in the form of large earthquake occurrence event. The partial release in second event of May 2015 of similar size shows that the physical process is trying to release the energy with large earthquake event. If it would have been in other regions like that of seismic gap region, the fault may not have released the energy and may be inviting even bigger event in future. It is, therefore, necessary to look into the seismicity from strain rates also for its due interpretation in terms of predicting the seismic hazard in various segments of Himalayas.  相似文献   

17.
采用β统计对汶川地震前后鄂尔多斯块体周缘地区的地震活动率进行了空间扫描分析,并采用JiChen的震源破裂模型计算了汶川地震产生的库仑破裂应力变化,以研究鄂尔多斯块体周缘地区近期地震活动性与汶川地震应力触发作用的关系。结果发现,鄂尔多斯块体西南缘弧形断裂束的南东段与南缘渭河盆地的地震活动率在汶川地震后提高显著,其他区域的地震活动率没有明显提高,库仑破裂应力计算得到两个区域的应力变化范围分别为0.005～0.02 MPa和0.001～0.01 MPa,表明汶川地震有可能触发了这两个区域的地震活动。鄂尔多斯块体东缘的山西断陷带处于库仑破裂应力计算的应力增加区,应力变化范围为0～0.012 MPa,2009年3月以来发生的4次ML4.5～5.2级强有感至微破坏地震有可能被汶川地震所延迟触发。b值、地震能量释放率与空间相关距离SCL等地震活动性参数随时间变化扫描结果显示,该区域可能处于不断趋近高应力累积的状态,其未来大震有可能提前发生。西缘地区为应力减小区,其目前的地震活动处于正常水平状态。  相似文献   

18.
Variations of seismic mode in the region of the Avachinsky Gulf (Kamchatka, Russia) are considered. Observed anomalies (seismic quiescence, the ring seismicity, reduction of the slope of the earthquake recurrence diagram) provide a basis to consider this region as a place of strong earthquake preparation. The Kamchatka regional catalogues of earthquakes between 1962–1995 were used in the analysis. A reduced seismicity rate is observed during 10 years in an area of 150 km × 60 km in size. During the last five years, in the vicinity of the area considered, earthquakes with M > 5 occurred three times more often than the average over thirty years. It is interpreted as ring seismicity. The block of 220 km × 220~km in size, including the quiescence zone, is characterized by a continuous decrease of the recurrence diagram slope, which has reached a minimum value for the last 33 years in this region.  相似文献   

19.
The Sannio-Matese region is one of the most seismically active regions of Italy and has been struck by large historical earthquakes. At present, the area is characterized by low magnitude background seismicity and small seismic sequences following M4 main events. In this paper, we show Vp and Vp/Vs models and 3D locations for a complete set of earthquakes occurring in the period 1991–2001. We observe a significant crustal heterogeneity, with large scale east-verging high Vp fault-related-folds, stacked by the Pliocene compression. The relocated earthquakes cluster along a 70° east-dipping, NW-striking plane located at the border of the high Vp thrust units. Normal fault earthquakes related to the young and active extension occur within these high Vp zones, interpreted as high strength material. We expect large future earthquakes to occur within these high Vp zones actually characterized by low magnitude seismicity at their borders.  相似文献   

20.
We studied the temporal behavior of the background shallow seismicity rate in 700 circular areas across inland Japan. To search for and test the significance of the possible rate changes in background seismicity, we developed an efficient computational method that applies the space–time ETAS model proposed by Ogata in 1998 to the areas. Also, we conducted Monte Carlo tests using a simulated catalog to validate the model we applied. Our first finding was that the activation anomalies were found so frequently that the constant background seismicity hypothesis may not be appropriate and/or the triggered event model with constraints on the parameters may not adequately describe the observed seismicity. However, quiescence occasionally occurs merely by chance. Another outcome of our study was that we could automatically find several anomalous background seismicity rate changes associated with the occurrence of large earthquakes. Very significant seismic activation was found before the M6.1 Mt. Iwate earthquake of 1998. Also, possible seismic quiescence was found in an area 150 km southwest of the focal region of the M7.3 Western Tottori earthquake of 2000. The seismicity rate in the area recovered after the mainshock.  相似文献   

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