The 2022 Menyuan M_(S)6.9 earthquake,which occurred on January 8,is the most destructive earthquake to occur near the Lenglongling(LLL)fault since the 2016 Menyuan M_(S)6.4 earthquake.We relocated the mainshock and af...The 2022 Menyuan M_(S)6.9 earthquake,which occurred on January 8,is the most destructive earthquake to occur near the Lenglongling(LLL)fault since the 2016 Menyuan M_(S)6.4 earthquake.We relocated the mainshock and aftershocks with phase arrival time observations for three days after the mainshock from the Qinghai Seismic Network using the double-difference method.The total length and width of the aftershock sequence are approximately 32 km and 5 km,respectively,and the aftershocks are mainly concentrated at a depth of 7-12 km.The relocated sequence can be divided into 18 km west and 13 km east segments with a boundary approximately 5 km east of the mainshock,where aftershocks are sparse.The east and west fault structures revealed by aftershock locations differ significantly.The west fault strikes EW and inclines to the south at a 71°-90°angle,whereas the east fault strikes 133°and has a smaller dip angle.Elastic strain accumulates at conjunctions of faults with different slip rates where it is prone to large earthquakes.Based on surface traces of faults,the distribution of relocated earthquake sequence and surface ruptures,the mainshock was determined to have occurred at the conjunction of the Tuolaishan(TLS)fault and LLL fault,and the west and east segments of the aftershock sequence were on the TLS fault and LLL fault,respectively.Aftershocks migrate in the early and late stages of the earthquake sequence.In the first 1.5 h after the mainshock,aftershocks expand westward from the mainshock.In the late stage,seismicity on the northeast side of the east fault is higher than that in other regions.The migration rate of the west segment of the aftershock sequence is approximately 4.5 km/decade and the afterslip may exist in the source region.展开更多
Using the double-difference relocation algo- rithm, we relocated the 20 April 2013 Lushan, Sichuan, earthquake (Ms 7.0), and its 4,567 aftershocks recorded during the period between 20 April and May 3, 2013. Our res...Using the double-difference relocation algo- rithm, we relocated the 20 April 2013 Lushan, Sichuan, earthquake (Ms 7.0), and its 4,567 aftershocks recorded during the period between 20 April and May 3, 2013. Our results showed that most aftershocks are relocated between 10 and 20 km depths, but some large aftershocks were relocated around 30 krn depth and small events extended upward near the surface. Vertical cross sections illustrate a shovel-shaped fault plane with a variable dip angle from the southwest to northeast along the fault. Furthermore, the dip angle of the fault plane is smaller around the mainshock than that in the surrounding areas along the fault. These results suggest that it may be easy to generate the strong earthquake in the place having a small dip angle of the fault, which is somewhat similar to the genesis of the 2008 Wenchuan earthquake. The Lushan mainshock is underlain by the seismically anomalous layers with low-Vp, low-Vs, and high-Poisson's ratio anomalies, possibly suggesting that the fluid-filled fractured rock matrices might signifi- cantly reduce the effective normal stress on the fault plane to bring the brittle failure. The seismic gap between Lushan and Wenchuan aftershocks is suspected to be vulnerable to future seismic risks at greater depths, if any.展开更多
Using the moment tensor inversion method, we calculate the focal mechanisms of the aftershock sequence of the Ms=6.1 Lulong earthquake occurred on October 19, 1982 in Hebei Province. We found that the pressure axis in...Using the moment tensor inversion method, we calculate the focal mechanisms of the aftershock sequence of the Ms=6.1 Lulong earthquake occurred on October 19, 1982 in Hebei Province. We found that the pressure axis in Lulong basin is nearly in the east-west direction with an azimuth of N74°E. However, in the north of the basin the stress axis changes to N43°E; and in some places near the center of the basin it changes to the northwest that is almost perpendicular to the P axis obtained by us from those events around the basin. This feature illuminates that in Lulong earthquake sequence, the stress direction is different in different parts of crustal structure, which shows that the tectonic movement in Lulong region is complex. This is because that Lulong is located in the eastern part of Chinese mainland and is subject to the compression of Japanese Sea Basin driven by the Pacific Plate. On the other hand, nipped by the Yanshan and North China blocks, Lulong is obviously restricted by the block boundaries.展开更多
Shallow earthquakes usually show obvious spatio-temporal clustering patterns. In this study, several spatio-temporal point process models are applied to investigate the clustering characteristics of the well-known Tan...Shallow earthquakes usually show obvious spatio-temporal clustering patterns. In this study, several spatio-temporal point process models are applied to investigate the clustering characteristics of the well-known Tangshan sequence based on classical empirical laws and a few assumptions. The relative fit of competing models is compared by Akalke Information Criterion. The spatial clustering pattern is well characterized by the model which gives the best fit to the data. A simulated aftershock sequence is generated by thinning algorithm and compared with the real seismicity.展开更多
The 2021 Qinghai Maduo M_(S)7.4 earthquake was one of the strongest earthquakes that occurred in the Bayan Har block of the Tibetan Plateau during the past 30 years,which spatially filled in the gap of strong earthqua...The 2021 Qinghai Maduo M_(S)7.4 earthquake was one of the strongest earthquakes that occurred in the Bayan Har block of the Tibetan Plateau during the past 30 years,which spatially filled in the gap of strong earthquake in the eastern section of the northern block boundary.In this study,the aftershock sequence within 8 days after the mainshock was relocated by double difference algorithm.The results show that the total length of the aftershock zone is approximately 170 km;the mainshock epicenter is located in the center of the aftershock zone,indicating a bilateral rupture.The aftershocks are mainly distributed along NWW direction with an overall strike of 285°.The focal depth profiles indicate that the seismogenic fault is nearly vertical and dips to southwest or northeast in different sections,indicating a complex geometry.There is an aftershock gap located to the southeast of the mainshock epicenter with a scale of approximately 20 km.At the eastern end of the aftershock zone,horsetaillike branch faults show the terminal effect of a large strike-slip fault.There is a NW-trending aftershock zone on the north side of the western section,which may be a branch fault triggered by the mainshock.The location of the aftershock sequence is close to the eastern section of the Kunlun Mountain Pass-Jiangcuo(KMPJ)fault.The sequence overlaps well with surface trace of the KMPJ fault.We speculate that the KMPJ fault is the main seismogenic fault of the M_(S)7.4 Maduo earthquake.展开更多
Based on data of earthquake sequences with Ms≥5.0 in Chinese mainland from 1970 to 2004, for different sequence types and different rupture modes of the main shock, the relationship between aftershock distribution si...Based on data of earthquake sequences with Ms≥5.0 in Chinese mainland from 1970 to 2004, for different sequence types and different rupture modes of the main shock, the relationship between aftershock distribution size R and the magnitude of the main shock Mo has been studied statistically. Considering the rupture mode of the main shock, we give the quantitative statistical relationships between R and Mo under 95% confidence level for different sequence typos. Qualitatively, lgR, the logarithm of the aftershock distribution size, is positively correlative to the M0, but the data distribution is dispersed. Viewing from different sequence typos, the correlation between R and M0 is very weak for isolated earthquake type (lET) sequence, R distributes in the range from 5 to 60 km; For mainshock-aftershock type (MAT), lgR is positively correlative to M0; For multiple main shock type (MMT), the corelation between lgR and M0 is not very obvious when M0≤6.2 and R distributes in the range from 5 to 70 km, while it shows a linear correlation when M0≥6.3. The statistical results also show that the occupational ratios of different sequence types for strike-slip and oblique slip are almost the same. But for dip-slip (mostly are thrust mechanisms), the ratio of MAT is higher than that of IET and MMT. Comparing with previous results, it indicates that, when M0 is large enough, R is mainly determined by M0 and there is almost no relationship with the rupture mode of the main shock.展开更多
The contained underground explosion (CUE) usually generates huge number of aftershocks. This kind of after-shocks induced by three CUEs was investigated in the paper. The conclusions show that the duration of aftersho...The contained underground explosion (CUE) usually generates huge number of aftershocks. This kind of after-shocks induced by three CUEs was investigated in the paper. The conclusions show that the duration of aftershock waveforms are rather short, 70 percent of them range from 2 to 7; the occurrences of the aftershocks conform to negative power function, which has the power of -1.6. The aftershock sequence attenuates a little bit faster, with power of -1.0, within two weeks of post-explosions. During the early stage of post-explosions the aftershocks show up in a cluster, however, they usually show up individually during the late stage of post-explosions. The number of aftershocks generated by the compatible explosions differs by several times because of different me-dium and geological structure; within one month after an explosion with Richater magnitude of 5.5, the number of aftershocks attenuates to the background. Hereafter there are still tiny numbers of aftershocks.展开更多
Earthquakes are one of the natural disasters that pose a major threat to human lives and property. Earthquake prediction propels the construction and development of modern seismology;however, current deterministic ear...Earthquakes are one of the natural disasters that pose a major threat to human lives and property. Earthquake prediction propels the construction and development of modern seismology;however, current deterministic earthquake prediction is limited by numerous difficulties. Identifying the temporal and spatial statistical characteristics of earthquake occurrences and constructing earthquake risk statistical prediction models have become significant;particularly for evaluating earthquake risks and addressing seismic planning requirements such as the design of cities and lifeline projects based on the obtained insight. Since the 21 st century, the occurrence of a series of strong earthquakes represented by the Wenchuan M8 earthquake in 2008 in certain low-risk prediction areas has caused seismologists to reflect on traditional seismic hazard assessment globally. This article briefly reviews the development of statistical seismology, emphatically analyzes the research results and existing problems of statistical seismology in seismic hazard assessment, and discusses the direction of its development. The analysis shows that the seismic hazard assessment based on modern earthquake catalogues in most regions should be effective. Particularly, the application of seismic hazard assessment based on ETAS(epidemic type aftershock sequence)should be the easiest and most effective method for the compilation of seismic hazard maps in large urban agglomeration areas and low seismic hazard areas with thick sedimentary zones.展开更多
基金jointly funded by the National Key Research and Development Program of China (No. 2021YFC3000702)the Special Fund of the Institute of Geophysics, China Earthquake Administration (No. DQJB21Z05)the National Natural Science Foundation of China (No. 41804062)
文摘The 2022 Menyuan M_(S)6.9 earthquake,which occurred on January 8,is the most destructive earthquake to occur near the Lenglongling(LLL)fault since the 2016 Menyuan M_(S)6.4 earthquake.We relocated the mainshock and aftershocks with phase arrival time observations for three days after the mainshock from the Qinghai Seismic Network using the double-difference method.The total length and width of the aftershock sequence are approximately 32 km and 5 km,respectively,and the aftershocks are mainly concentrated at a depth of 7-12 km.The relocated sequence can be divided into 18 km west and 13 km east segments with a boundary approximately 5 km east of the mainshock,where aftershocks are sparse.The east and west fault structures revealed by aftershock locations differ significantly.The west fault strikes EW and inclines to the south at a 71°-90°angle,whereas the east fault strikes 133°and has a smaller dip angle.Elastic strain accumulates at conjunctions of faults with different slip rates where it is prone to large earthquakes.Based on surface traces of faults,the distribution of relocated earthquake sequence and surface ruptures,the mainshock was determined to have occurred at the conjunction of the Tuolaishan(TLS)fault and LLL fault,and the west and east segments of the aftershock sequence were on the TLS fault and LLL fault,respectively.Aftershocks migrate in the early and late stages of the earthquake sequence.In the first 1.5 h after the mainshock,aftershocks expand westward from the mainshock.In the late stage,seismicity on the northeast side of the east fault is higher than that in other regions.The migration rate of the west segment of the aftershock sequence is approximately 4.5 km/decade and the afterslip may exist in the source region.
基金supported by the National Natural Scientific Foundation of China (41274059 and 40974021)Beijing Natural Scientific Foundation (8122039 and 8092028) to J. LeiSpecial Project for Basic Scientific Research (ZDJ2013-12) to G. Zhang
文摘Using the double-difference relocation algo- rithm, we relocated the 20 April 2013 Lushan, Sichuan, earthquake (Ms 7.0), and its 4,567 aftershocks recorded during the period between 20 April and May 3, 2013. Our results showed that most aftershocks are relocated between 10 and 20 km depths, but some large aftershocks were relocated around 30 krn depth and small events extended upward near the surface. Vertical cross sections illustrate a shovel-shaped fault plane with a variable dip angle from the southwest to northeast along the fault. Furthermore, the dip angle of the fault plane is smaller around the mainshock than that in the surrounding areas along the fault. These results suggest that it may be easy to generate the strong earthquake in the place having a small dip angle of the fault, which is somewhat similar to the genesis of the 2008 Wenchuan earthquake. The Lushan mainshock is underlain by the seismically anomalous layers with low-Vp, low-Vs, and high-Poisson's ratio anomalies, possibly suggesting that the fluid-filled fractured rock matrices might signifi- cantly reduce the effective normal stress on the fault plane to bring the brittle failure. The seismic gap between Lushan and Wenchuan aftershocks is suspected to be vulnerable to future seismic risks at greater depths, if any.
基金National Natural Science Foundation of China(40234038)
文摘Using the moment tensor inversion method, we calculate the focal mechanisms of the aftershock sequence of the Ms=6.1 Lulong earthquake occurred on October 19, 1982 in Hebei Province. We found that the pressure axis in Lulong basin is nearly in the east-west direction with an azimuth of N74°E. However, in the north of the basin the stress axis changes to N43°E; and in some places near the center of the basin it changes to the northwest that is almost perpendicular to the P axis obtained by us from those events around the basin. This feature illuminates that in Lulong earthquake sequence, the stress direction is different in different parts of crustal structure, which shows that the tectonic movement in Lulong region is complex. This is because that Lulong is located in the eastern part of Chinese mainland and is subject to the compression of Japanese Sea Basin driven by the Pacific Plate. On the other hand, nipped by the Yanshan and North China blocks, Lulong is obviously restricted by the block boundaries.
基金supported by National Natural Science of Foundation of China(No.10871026)
文摘Shallow earthquakes usually show obvious spatio-temporal clustering patterns. In this study, several spatio-temporal point process models are applied to investigate the clustering characteristics of the well-known Tangshan sequence based on classical empirical laws and a few assumptions. The relative fit of competing models is compared by Akalke Information Criterion. The spatial clustering pattern is well characterized by the model which gives the best fit to the data. A simulated aftershock sequence is generated by thinning algorithm and compared with the real seismicity.
基金supported by the National Key R&D Program of China(Grant No.2018YFC1504103)the National Natural Science Foundation of China(Grant No.41774067)+1 种基金the Special Fund of the Institute of Geophysics,China Earthquake Administration(Grant No.DQJB20X07)S&T Program of Qinghai Province(Grant No.2020-ZJ-752).
文摘The 2021 Qinghai Maduo M_(S)7.4 earthquake was one of the strongest earthquakes that occurred in the Bayan Har block of the Tibetan Plateau during the past 30 years,which spatially filled in the gap of strong earthquake in the eastern section of the northern block boundary.In this study,the aftershock sequence within 8 days after the mainshock was relocated by double difference algorithm.The results show that the total length of the aftershock zone is approximately 170 km;the mainshock epicenter is located in the center of the aftershock zone,indicating a bilateral rupture.The aftershocks are mainly distributed along NWW direction with an overall strike of 285°.The focal depth profiles indicate that the seismogenic fault is nearly vertical and dips to southwest or northeast in different sections,indicating a complex geometry.There is an aftershock gap located to the southeast of the mainshock epicenter with a scale of approximately 20 km.At the eastern end of the aftershock zone,horsetaillike branch faults show the terminal effect of a large strike-slip fault.There is a NW-trending aftershock zone on the north side of the western section,which may be a branch fault triggered by the mainshock.The location of the aftershock sequence is close to the eastern section of the Kunlun Mountain Pass-Jiangcuo(KMPJ)fault.The sequence overlaps well with surface trace of the KMPJ fault.We speculate that the KMPJ fault is the main seismogenic fault of the M_(S)7.4 Maduo earthquake.
基金Joint Seismological Science Foundation of China(105076)continued subject″Statistical Features of Aftershock Sequences and Forecastof the Large Aftershocks″(2004BA601B01-04-02)Ministry of Science and Technology of Chinain the 10th Five-year Plan.
文摘Based on data of earthquake sequences with Ms≥5.0 in Chinese mainland from 1970 to 2004, for different sequence types and different rupture modes of the main shock, the relationship between aftershock distribution size R and the magnitude of the main shock Mo has been studied statistically. Considering the rupture mode of the main shock, we give the quantitative statistical relationships between R and Mo under 95% confidence level for different sequence typos. Qualitatively, lgR, the logarithm of the aftershock distribution size, is positively correlative to the M0, but the data distribution is dispersed. Viewing from different sequence typos, the correlation between R and M0 is very weak for isolated earthquake type (lET) sequence, R distributes in the range from 5 to 60 km; For mainshock-aftershock type (MAT), lgR is positively correlative to M0; For multiple main shock type (MMT), the corelation between lgR and M0 is not very obvious when M0≤6.2 and R distributes in the range from 5 to 70 km, while it shows a linear correlation when M0≥6.3. The statistical results also show that the occupational ratios of different sequence types for strike-slip and oblique slip are almost the same. But for dip-slip (mostly are thrust mechanisms), the ratio of MAT is higher than that of IET and MMT. Comparing with previous results, it indicates that, when M0 is large enough, R is mainly determined by M0 and there is almost no relationship with the rupture mode of the main shock.
文摘The contained underground explosion (CUE) usually generates huge number of aftershocks. This kind of after-shocks induced by three CUEs was investigated in the paper. The conclusions show that the duration of aftershock waveforms are rather short, 70 percent of them range from 2 to 7; the occurrences of the aftershocks conform to negative power function, which has the power of -1.6. The aftershock sequence attenuates a little bit faster, with power of -1.0, within two weeks of post-explosions. During the early stage of post-explosions the aftershocks show up in a cluster, however, they usually show up individually during the late stage of post-explosions. The number of aftershocks generated by the compatible explosions differs by several times because of different me-dium and geological structure; within one month after an explosion with Richater magnitude of 5.5, the number of aftershocks attenuates to the background. Hereafter there are still tiny numbers of aftershocks.
基金This work was supported by the National Natural Science Foundation of China(Grant No.U2039204)the National Key R&D Program of China(Grant No.2018YFC1504203).
文摘Earthquakes are one of the natural disasters that pose a major threat to human lives and property. Earthquake prediction propels the construction and development of modern seismology;however, current deterministic earthquake prediction is limited by numerous difficulties. Identifying the temporal and spatial statistical characteristics of earthquake occurrences and constructing earthquake risk statistical prediction models have become significant;particularly for evaluating earthquake risks and addressing seismic planning requirements such as the design of cities and lifeline projects based on the obtained insight. Since the 21 st century, the occurrence of a series of strong earthquakes represented by the Wenchuan M8 earthquake in 2008 in certain low-risk prediction areas has caused seismologists to reflect on traditional seismic hazard assessment globally. This article briefly reviews the development of statistical seismology, emphatically analyzes the research results and existing problems of statistical seismology in seismic hazard assessment, and discusses the direction of its development. The analysis shows that the seismic hazard assessment based on modern earthquake catalogues in most regions should be effective. Particularly, the application of seismic hazard assessment based on ETAS(epidemic type aftershock sequence)should be the easiest and most effective method for the compilation of seismic hazard maps in large urban agglomeration areas and low seismic hazard areas with thick sedimentary zones.