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1.
In the region of Three Gorges Reservoir (TGR) in China, there has been occurrence of several frequent earthquakes of moderate intensity since reservoir impounding occurred in 2003. These earthquakes are generally believed to be induced by reservoir impoundment and water-level variations. Usually, the geo-stress will change, when natural earthquakes occur. Following this principle, this paper adopted the rate and state theory to simulate and estimate Coulomb stress changes in the TGR region and obtained the pattern of Coulomb stress changes with time and the event sequence as well as the distribution of Coulomb stress changes in space. First, the TGR regional catalogue was analyzed and processed, leading to quantification of the magnitude of completeness and all of the parameters that are used in the stress–seismicity inversion process, including the reference seismicity rates, characteristic relaxation time, fault constitutive parameters, and stress rates. Second, the temporal evolution of the stress changes in different time windows was computed and analyzed, and it was found that there is an association between the Coulomb stress changes and rates of increase in the cumulative number of earthquakes. In addition, the earthquake occurred in November 2008 (M S = 4.1) was analyzed and attempted to simulate the distribution of stress changes in space through the stress–seismicity inversion model. The results proved that the modeled area coincides with the historical area of earthquakes that occurred after 2008. Finally, a prediction was made about the earthquake productivity rates after 2015, which showed a declining earthquake rate over time that ultimately returned to the background seismicity. This result is essentially in agreement with Omori’s law. To conclude, it is rational to use the stress-inversion method to analyze the relationship between induced earthquake seismicity and local stress changes as well as to simulate the area of earthquake occurrence and productivity rates of reservoir-induced earthquakes.  相似文献   

2.
Seismic hazard analysis of the northwest Himalayan belt was carried out by using extreme value theory (EVT). The rate of seismicity (a value) and recurrence intervals with the given earthquake magnitude (b value) was calculated from the observed data using Gutenberg–Richter Law. The statistical evaluation of 12,125 events from 1902 to 2017 shows the increasing trend in their inter-arrival times. The frequency–magnitude relation exhibits a linear downslope trend with negative slope of 0.8277 and positive intercept of 4.6977. The empirical results showed that the annual risk probability of high magnitude earthquake M?≥?7.7 in 50 years is 88% with recurrence period of 47 years, probability of M?≤?7.5 in 50 years is 97% with recurrence period of 27 years, and probability of M?≤?6.5 in 50 years is 100% with recurrence period of 4 years. Kashmir valley, located in the NW Himalaya, encompasses a peculiar tectonic and structural setup. The patterns of the present and historical seismicity records of the valley suggest a long-term strain accumulation along NNW and SSE extensions with the decline in the seismic gap, posing a potential threat of earthquakes in the future. The Kashmir valley is characterized by the typical lithological, tectono-geomorphic, geotechnical, hydrogeological and socioeconomic settings that augment the earthquake vulnerability associated with the seismicity of the region. The cumulative impact of the various influencing parameters therefore exacerbates the seismic hazard risk of the valley to future earthquake events.  相似文献   

3.
In this study, the seismicity rate changes that can represent an earthquake precursor were investigated along the Sagaing Fault Zone (SFZ), Central Myanmar, using the Z value technique. After statistical improvement of the existing seismicity data (the instrumental earthquake records) by removal of the foreshocks and aftershocks and man-made seismicity changes and standardization of the reported magnitude scales, 3574 earthquake events with a M w ≥ 4.2 reported during 1977–2015 were found to directly represent the seismotectonic activities of the SFZ. To find the characteristic parameters specifically suitable for the SFZ, seven known events of M w ≥ 6.0 earthquakes were recognized and used for retrospective tests. As a result, utilizing the conditions of 25 fixed earthquake events considered (N) and a 2-year time window (T w), a significantly high Z value was found to precede most of the M w ≥ 6.0 earthquakes. Therefore, to evaluate the prospective areas of upcoming earthquakes, these conditions (N = 25 and T w = 2) were applied with the most up-to-date seismicity data of 2010–2015. The results illustrate that the vicinity of Myitkyina and Naypyidaw (Z = 4.2–5.1) cities might be subject to strong or major earthquakes in the future.  相似文献   

4.
Transition from subduction of normal to thickened oceanic crust occurs in the central portion of the Costa Rican margin, where large interplate earthquakes (M ~ 7) and abundant interseismic seismicity have been associated with subduction of bathymetric highs. We relocated ~1,300 earthquakes recorded for 6 months by a combined on- and offshore seismological network using probabilistic earthquake relocation in a 3D P-wave velocity model. Most of the seismicity originated at the seismogenic zone of the plate boundary, appearing as an 18° dipping, planar cluster from 15 to 25–30 km depth, beneath the continental shelf. Several reverse focal mechanisms were resolved within the cluster. The upper limit of this interseismic interplate seismicity seems to be controlled primarily by the overlying-plate thickness and coherency, which in turn is governed by the erosional processes and fluid release and escape at temperatures lower than ~100 to 120 °C along the plate boundary. The downdip limit of the stick–slip behaviour collocates with relative low temperatures of ~150 to 200 °C, suggesting that it is controlled by serpentinization of the mantle wedge. The distribution of the interseismic interplate seismicity is locally modified by the presence of subducted seamounts at different depths. Unlike in northern Costa Rica, rupture of large earthquakes in the last two decades seems to coincide with the area defined by the interseismic interplate seismicity.  相似文献   

5.
The frequency–magnitude distributions of earthquakes are used in this study to estimate the earthquake hazard parameters for individual earthquake source zones within the Mainland Southeast Asia. For this purpose, 13 earthquake source zones are newly defined based on the most recent geological, tectonic, and seismicity data. A homogeneous and complete seismicity database covering the period from 1964 to 2010 is prepared for this region and then used for the estimation of the constants, a and b, of the frequency–magnitude distributions. These constants are then applied to evaluate the most probable largest magnitude, the mean return period, and the probability of earthquake of different magnitudes in different time spans. The results clearly show that zones A, B, and E have the high probability for the earthquake occurrence comparing with the other seismic zones. All seismic source zones have 100 % probability that the earthquake with magnitude ≤6.0 generates in the next 25 years. For the Sagaing Fault Zone (zones C), the next Mw 7.2–7.5 earthquake may generate in this zone within the next two decades and should be aware of the prospective Mw 8.0 earthquake. Meanwhile, in Sumatra-Andaman Interplate (zone A), an earthquake with a magnitude of Mw 9.0 can possibly occur in every 50 years. Since an earthquake of magnitude Mw 9.0 was recorded in this region in 2004, there is a possibility of another Mw 9.0 earthquake within the next 50 years.  相似文献   

6.
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   

7.
Seismic hazard assessment of slow active fault zones is challenging as usually only a few decades of sparse instrumental seismic monitoring is available to characterize seismic activity. Tectonic features linked to the observed seismicity can be mapped by seismic imaging techniques and/or geomorphological and structural evidences. In this study, we investigate a seismic lineament located in the Swiss Alpine foreland, which was discussed in previous work as being related to crustal structures carrying in size the potential of a magnitude M 6 earthquake. New, low-magnitude (?2.0 ≤ ML ≤ 2.5) earthquake data are used to image the spatial and temporal distribution of seismogenic features in the target area. Quantitative and qualitative analyses are applied to the waveform dataset to better constrain earthquakes distribution and source processes. Potential tectonic features responsible for the observed seismicity are modelled based on new reinterpretations of oil industry seismic profiles and recent field data in the study area. The earthquake and tectonic datasets are then integrated in a 3D model. Spatially, the seismicity correlates over 10–15 km with a N–S oriented sub-vertical fault zone imaged in seismic profiles in the Mesozoic cover units above a major decollement on top of the mechanically more rigid basement and seen in outcrops of Tertiary series east of the city of Fribourg. Observed earthquakes cluster at shallow depth (<4 km) in the sedimentary cover. Given the spatial extend of the observed seismicity, we infer the potential of a moderate size earthquake to be generated on the lineament. However, since the existence of along strike structures in the basement cannot be excluded, a maximum M 6 earthquake cannot be ruled out. Thus, the Fribourg Lineament constitutes a non-negligible source of seismic hazard in the Swiss Alpine foreland.  相似文献   

8.
The instrumental seismicity that occurred in the Jordan Dead Sea transform region during the period 1900–2014 is compiled from all available sources. Some 492 phosphate mining explosions (M ≤ 3.9) are recognized and filtered from the data. Excluding these, it is found that 4448 earthquakes have occurred with magnitudes M ≥ 3.0. Only 572, 18 and 2 of these had magnitudes M ≥ 4, 5, and 6 in respective order. Average recurrence periods for the 5 and 6 magnitudes are 6.3 and 57 years. Much of these have occurred in sequences and swarms. The epicentral distribution of the compiled instrumental seismicity data shows very good correlation with the general tectonics of the study region. All tectonic elements are active in the present with a noticeable hazard. The regional strike-slip faults of the transform proper remain the major sources of this hazard. They account for not less than 99% of the seismic energy released from all instrumental data. The calculated a-parameter of the whole transform is 6.6. It varies for all its strike-slip faults mostly in the range 6.0–6.6. The b-value of the whole transform and some of its major segments is 1.0. Others show b-variations in the range of 1.1–1.3. Such a- and b-values imply recurrence periods of 38 years and 395 years for the 6 and 7 magnitude earthquakes. Such values, their variations and the seismic moment calculations clearly indicate an appreciable level of seismic hazard associated with all segments. This hazard appears to be highest for Al Ghab segment, followed by Beqa’a and Wadi Araba segments, respectively. The other three segments appear to be of lower hazard. The seismicity of this region is very shallow. More than 99% of the seismic energy has been released from the brittle granitic upper crust whose thickness is about 21 km and its Poisson’s ratio is 0.25. More than 93.6% of the energy was released from its upper 10 km. Very little energy is released from the underlying ductile basaltic crust whose Poisson’s ratio is 0.29. The calculated seismic slip rate along the Whole Jordan Dead Sea transform is 0.54 cm/year if the fault depth is assumed 10 km. It increases to 0.77 and 1.07 cm/year if the fault depth is reduced to 7 and 5 km, respectively. These slip rates are comparable with the long-term geologically deduced rate of 1 cm/year.  相似文献   

9.
Before starting seismic cycle of Ahar–Varzaghan 2012 event, a partial gap in the form of a pre-seismic calm sequence (seismicity rate, r = 0.46 event/year, b = 1.4) with duration of 303 days spatially has dominated over the entire seismogenic area. From April 17, 2012, to May 31, 2012, r significantly increased to 2.16, indicating strong foreshock sequence, and b value changed to 1.9, remarkably. In the last two months before the mainshock, foreshocks have partially migrated toward the earthquake fault (with a decrease in size, b = 2.0). Significantly, high rate of seismicity and low V P /V S (1.64) in the foreshocks sequence and also very high seismicity rate (17.3) and high V P /V S (1.76) in the aftershocks sequence make substantial differences between the seismic cycle and the background seismicity. Moreover, a significant E–W migration of the microseismicity was confirmed in the study area.  相似文献   

10.
We estimate the energetic and spatial characteristics of seismicity in the Algeria–Morocco region using a variety of seismic and statistical parameters, as a first step in a detailed investigation of regional seismic hazard. We divide the region into five seismotectonic regions, comprising the most important tectonic domains in the studied area: the Moroccan Meseta, the Rif, the Tell, the High Plateau, and the Atlas. Characteristic seismic hazard parameters, including the Gutenberg–Richter b-value, mean seismic activity rate, and maximum possible earthquake magnitude, were computed using an extension of the Aki–Utsu procedure for incomplete earthquake catalogs for each domain, based on recent earthquake catalogs compiled for northern Morocco and northern Algeria. Gutenberg–Richter b-values for each zone were initially estimated using the approach of Weichert (Bull Seismol Soc Am 70:1337–1346, 1980): the estimated b-values are 1.04 ± 0.04, 0.93 ± 0.10, 0.72 ± 0.03, 0.87 ± 0.02, and 0.77 ± 0.02 for the Atlas, Meseta, High Plateau, Rif, and Tell seismogenic zones, respectively. The fractal dimension D 2 was also estimated for each zone. From the ratio D 2/b, it appears that the Tell and Rif zones, with ratios of 2.09 and 2.12, respectively, have the highest potential earthquake hazard in the region. The Gutenberg–Richter relationship analysis allows us to derive that in the Tell and Rif, the number of earthquake with magnitude above Mw 4.0, since 1925 normalized to decade and to square cell with 100-km sides is equal to 2.6 and 1.91, respectively. This study provides the first detailed information about the potential seismicity of these large domains, including maximum regional magnitudes, characteristics of spatial clustering, and distribution of seismic energy release.  相似文献   

11.

Complexity in the earthquake mechanism is manifested in different forms such as fractal distribution, clustering of seismicity, etc., and characterized as critical phenomenon. Occurrences of earthquakes generally represent the state of metastable equilibrium. The Andaman–Sumatra subduction zone is one of the most seismically active corridors (possibly in metastable state) in the world. Recently, the region faced three major earthquakes of magnitude more than 8.5 (M ~ 9.1 on December 26, 2004; M ~ 8.6 on March 28, 2005; M ~ 8.6 on April 11, 2012). Researchers have suggested multiple causes of earthquake generation in this region including the one with possible correlation of tidal stresses with earthquake occurrences. The latter issue, however, has been hotly debated in view of the fact that a small stress generated due to tidal forcing cannot cause such a bigger magnitude earthquake. We study here the impact of tidal forcing on critically generated earthquake phenomena. We examined the statistical behavior of recurrence time interval of earthquakes using the available data for period of about 40 years from 1973 to 2013. We constrain the simple empirical toy model using the concept of catastrophe theory to evaluate the impact of small tidal forcing on the critical state of earthquakes occurrences. In addition to the major role of Helmholtz free energy during the plate motion, our analysis suggests that the stability and critical behavior of the earthquake in Sumatra region could be associated with tidal forcing, however, only for triggering of some of the “Catastrophic–Chaotic” earthquake phenomenon.

  相似文献   

12.
Complexity in the earthquake mechanism is manifested in different forms such as fractal distribution, clustering of seismicity, etc., and characterized as critical phenomenon. Occurrences of earthquakes generally represent the state of metastable equilibrium. The Andaman–Sumatra subduction zone is one of the most seismically active corridors (possibly in metastable state) in the world. Recently, the region faced three major earthquakes of magnitude more than 8.5 (M ~ 9.1 on December 26, 2004; M ~ 8.6 on March 28, 2005; M ~ 8.6 on April 11, 2012). Researchers have suggested multiple causes of earthquake generation in this region including the one with possible correlation of tidal stresses with earthquake occurrences. The latter issue, however, has been hotly debated in view of the fact that a small stress generated due to tidal forcing cannot cause such a bigger magnitude earthquake. We study here the impact of tidal forcing on critically generated earthquake phenomena. We examined the statistical behavior of recurrence time interval of earthquakes using the available data for period of about 40 years from 1973 to 2013. We constrain the simple empirical toy model using the concept of catastrophe theory to evaluate the impact of small tidal forcing on the critical state of earthquakes occurrences. In addition to the major role of Helmholtz free energy during the plate motion, our analysis suggests that the stability and critical behavior of the earthquake in Sumatra region could be associated with tidal forcing, however, only for triggering of some of the “Catastrophic–Chaotic” earthquake phenomenon.  相似文献   

13.
China has a long history of earthquake records. The Shanxi rift system (SRS) is situated along the axial zone of the domal uplift of the Shanxi Highlands and is the boundary between the Ordos block and the North China Plain block. Strong earthquakes in the SRS have been recorded since the thirteenth century. In our work, we applied the Bayesian probability method using extreme value distribution of earthquake occurrences to estimate the seismic hazard in the SRS. The seismic moment, slip rate, earthquake recurrence rate, and magnitude were considered as the basic parameters for computing the Bayesian prior estimates of the seismicity. These estimates were then updated in terms of Bayes’ theorem and historical estimates of seismicity in the SRS. The probability of occurrence of $M_{\text{s}} = 5.0$ for Z1, Z2, and Z3 is less than 0.3, 0.1, and 0.6, respectively (T = 5 years). The probability of the occurrence of M  $\ge$  8.0 is small for the whole SRS. The selection of upper bound magnitude probably influences the result, and the upper bound magnitude of Z1, Z2, and Z3 may be 7.5, 7.0, and 8.5, respectively. We obtained the values of the magnitude of completeness M c (3.2) and the Gutenberg–Richter b value before applying the Bayesian extreme value distribution of earthquake occurrences method.  相似文献   

14.
Climate change in the Great Lakes Basin of North America over the next several decades is projected to lead to significant changes to coastal environments. Groundwater-driven coastal bluff recession should increase in areas where groundwater forcing is important and lead to increased loss of coastal uplands. The latter is an issue in NW Pennsylvania because of coastal development pressures, and because the state ranks within the top five US states in grape production, most of which occurs within 5 km of the Lake Erie coastline. In 2007, viticulture contributed almost $2.4 billion to the state economy. An analysis of a 20-km stretch of coast shows that bluff retreat is pervasive and variable under current climatic conditions. Over a 9-year time frame, bluff change rates ranged from ?4.2 to +0.98 m/year. In general, higher retreat rates (?0.2 to ?0.65 m/year) occurred along the sandy central beach–ridge sector which lacks significant surface drainage. Lower retreat rates (?0.10 to ?0.25 m/year) occurred along coastal sectors where surface drainage networks are well developed. Conservative estimates of groundwater discharge at the bluff correlate strongly (r = 0.74, p < 0.001) with bluff retreat rate. Groundwater is inferred to be the principal driving mechanism for both bluff retreat and spatial variability in retreat rates on this coast. Other common factors that may spatially influence bluff retreat elsewhere (bluff height, land use, beach width) do not correlate strongly with retreat rate.  相似文献   

15.
Seismic risk assessment of the 3rd Azerbaijan gas pipeline in Iran   总被引：1，自引：1，他引：0  
A comprehensive seismic risk assessment has been performed for the existing route of the 3rd Azerbaijan natural gas buried pipeline in Iran. The major active seismic sources along the pipeline were identified and the geometrical parameters as well as the seismicity rates were determined. The seismic hazard assessment of the ground vibrations along the pipeline was performed in the framework of the Probabilistic Seismic Hazard Analysis using the CRISIS 2007 software. All of the components of the gas pipeline along the route were identified and the corresponding fragility functions are established through the methodology described in the HAZUS guideline (HAZUS MH MR4 Technical manual 2007 Department of homeland security emergency. Preparedness and Response Directorate, FEMA). A detailed cost analyses was taken into consideration based on the expert opinions in the National Iranian Gas Company, in order to provide more practical loss model for the pipeline route. Also, a simple method is suggested in order to account for the vent gas in the total loss estimation. The spatial analysis of the hazard function layer in combination with the loss model layer, in Geographical Information System  (GIS) platform, reveal the financial consequences of different earthquake scenarios.  相似文献   

16.
New data on seismically triggered soft-sediment deformation structures in Pleniglacial to Late Glacial alluvial fan and aeolian sand-sheet deposits of the upper Senne area link this soft-sediment deformation directly to earthquakes generated along the Osning Thrust, which is one of the major fault systems in Central Europe. Soft-sediment deformation structures include a complex fault and fold pattern, clastic dikes, sand volcanoes, sills, irregular intrusive sedimentary bodies, flame structures, and ball-and-pillow structures. The style of soft-sediment deformation will be discussed with respect to brittle failure, liquefaction and fluidization processes, and was controlled by (1) the magnitude of the earthquake and (2) the permeability, tensile strength and flexural resistance of the alluvial and aeolian sediments. It is the first time in northern Germany that fluidization and liquefaction features can be directly related to a fault. The occurrence of seismicity in the Late Pleistocene and in the seventeenth century indicates ongoing crustal movements along the Osning Thrust and sheds new light on the seismic activity of northern Germany. The Late Pleistocene earthquake probably occurred between 15.9 ± 1.6 and 13.1 ± 1.5 ka; the association of soft-sediment deformation structures implies that it had a magnitude of at least 5.5.  相似文献   

17.
We performed a probabilistic analysis of earthquake hazard input parameters, NW Turkey covers Gelibolu and Biga Peninsulas, and its vicinity based on four seismic sub-zones. The number of earthquakes with magnitude M ≥ 3.0 occurred in this region for the period between 1912 and 2007 is around 5130. Four seismic source sub-zones were defined with respect to seismotectonic framework, seismicity and fault geometry. The hazard perceptibility characterization was examined for each seismic source zone and for the whole region. The probabilities of earthquake recurrences were obtained by using Poisson statistical distribution models. In order to determine the source zones where strong and destructive earthquakes may occur, distribution maps for a, b and a/b values were calculated. The hazard scaling parameters (generally known as a and b values) in the computed magnitude–frequency relations vary in the intervals 4.28–6.58 and 0.59–1.13, respectively, with a RMS error percentage below 10 %. The lowest b value is computed for sub-zone three indicating the predominance of large earthquakes mostly at Gelibolu (Gallipoli) and north of Biga Peninsula (southern Marmara region), and the highest b value is computed for sub-zone two Edremit Bay (SW Marmara region). According to the analysis of each seismic sub-zone, the greatest risk of earthquake occurrence is determined for the triangle of Gelibolu–Tekirda? western part of Marmara Sea. Earthquake occurrence of the largest magnitude with 7.3 within a 100-year period was determined to be 46 % according to the Poisson distribution, and the estimated recurrence period of years for this region is 50 ± 12. The seismic hazard is pronounced high in the region extending in a NW–SE direction, north of Edremit Bay, west of Saros Bay and Yenice Gönen (southern Marmara region) in the south. High b values are generally calculated at depths of 5–20 km that can be expressed as low seismic energy release and evaluated as the seismogenic zone.  相似文献   

18.
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   

19.
We estimated spatio-temporal evolution of Coulomb stress within the subducted Pacific slab in Hokkaido from the analysis of seismicity rate change. For this purpose we used earthquake catalog from the Institute of Seismology and Volcanology (ISV), Hokkaido University for the period 1993/4/1–2006/12/31 after relocating to compensate location errors due to the heterogeneous P- and S-wave structure beneath Hokkaido. We found that spatial pattern of Coulomb stress change inverted from the seismicity rate change is comparable with static change in Coulomb stress estimated from dislocation models. Our results and analyses reveal important insights on spatio-temporal pattern of deformation of the subducted Pacific slab in terms of Coulomb stress change. We found that the 2003 Tokachi Oki earthquake (Mw = 8.0) pervasively perturbed Coulomb stress in a regional scale with a significant impact to trigger the 2004 Kushiro Oki earthquake. The 2004 Kushiro Oki earthquake (Mw = 7.0) is another significant stressing event that changed the pattern of Coulomb stress in the area. We found that stressing events with magnitude smaller than 7.0 has minimal impact on Coulomb stress change in the Pacific slab. Similarly, comparatively deep focused large earthquakes could not change Coulomb stress significantly. Further the pattern of Coulomb stress change after the 2003 Tokachi Oki earthquake correlates the pattern of afterslip distribution in Hokkaido.  相似文献   

20.
The Sichuan – Yunnan region is divided into nine active secondary crustal blocks, based on several GPS repeat surveys at more than 200 GPS sites during the period 1999 – 2005. Velocities of the nine secondary blocks are calculated and analysed. The strain field within the area related to the 2004 Sumatra – Andaman earthquake event is also analysed. Results indicate that the crustal movement in the northern and western areas of the Sichuan – Yunnan region is stronger than that in the south and east. The horizontal velocities change from 19 – 20 mm/y in the northern and the central rhombic block to 11.7 mm/y in the southern rhombic block. The orientations of block motion vary from 99° in the north to 126 – 150° in the central area and 156 – 188° in the south, implying that the motion of the Sichuan – Yunnan rhombic block is dominated by a clockwise rotation. The velocity differences between blocks inside and outside the rhombic block are about 6.5 – 7.7 mm/y in the northern and central Sichuan – Yunnan region. The southeastward extrusion rate of the Tibetan Plateau shows a remarkable downtrend of up to 47% along the Xianshuihe Fault, suggesting an increase in strain accumulation and hence an area prone to strong earthquakes. The horizontal coseismic deformation caused by the Mw9.0 Sumatra – Andaman earthquake is <10 mm with a south-southeast orientation towards the earthquake epicentre. The dilatational strain rates from coseismic displacements reveal a possible interaction between the extrusion from the Tibet plateau interior and the underthrust effects from the Sumatra – Andaman earthquake.  相似文献   

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