Repeating microearthquakes were identified along the edge of the rupture area of the 2008 MW7.9 Wenchuan earthquake. Slip rates at depths derived from seismic moments and recurrence intervals are found to be systemati...Repeating microearthquakes were identified along the edge of the rupture area of the 2008 MW7.9 Wenchuan earthquake. Slip rates at depths derived from seismic moments and recurrence intervals are found to be systematically larger than those observed at surface. This large deep slip rate may explain the odds about the occurrence of this unanticipated event. Our observations here suggested that seismic hazard could be underestimated if surface measurements alone are employed.展开更多
A shallow crustal velocity structure(above 10 km depth) is essential for understanding the crustal structures and deformation and assessing the exploration prospect of natural resources, and also provides priori infor...A shallow crustal velocity structure(above 10 km depth) is essential for understanding the crustal structures and deformation and assessing the exploration prospect of natural resources, and also provides priori information for imaging deeper crustal and mantle structure. Passive-source seismic methods are cost-effective and advantageous for regional-scale imaging of shallow crustal structures compared to active-source methods. Among these passive methods, techniques utilizing receiver function waveforms and/or body-wave amplitude ratios have recently gained prominence due to their relatively high spatial resolution. However, in basin regions, reverberations caused by near-surface unconsolidated sedimentary layers often introduce strong non-uniqueness and uncertainty, limiting the applicability of such methods. To address these challenges, we propose a two-step inversion method that uses multi-frequency P-RF waveforms and P-RF horizontal-to-vertical amplitude ratios. Synthetic tests indicate that our two-step inversion method can mitigate the non-uniqueness of the inversion and enhance the stability of the results. Applying this method to teleseismic data from a linear seismic array across the sedimentary basins in Northeast China, we obtain a high-resolution image of the shallow crustal S-wave velocity structure along the array. Our results reveal significant differences between the basins and mountains. The identification of low-velocity anomalies(<2.8 km s^(-1)) at depths less than 1.0 km beneath the Erlian Basin and less than 2.5 km beneath the Songliao Basin suggests the existence of sedimentary layers. Moreover, the high-velocity anomalies(~3.4–3.8 km s^(-1)) occurring at depths greater than 7 km in the Songliao Basin may reflect mafic intrusions emplaced during the Early Cretaceous. Velocity anomaly distribution in our imaging result is consistent with the location of the major faults, uplifts, and sedimentary depressions, as well as active-source seismic results. This application further validates the effectiveness of our method in constraining the depth-dependent characteristics of the S-wave velocity in basins with unconsolidated sedimentary cover.展开更多
Most earthquake loss studies use an inventory approach by which the predicted damages in various categories of structures and facilities in a concerned region are estimated and added together to obtain the total estim...Most earthquake loss studies use an inventory approach by which the predicted damages in various categories of structures and facilities in a concerned region are estimated and added together to obtain the total estimated. Such an approach requires a detailed inventory database of the structures and facilities in the region, which is not always readily available in many regions of the world. Therefore, an alternative means of estimating earthquake losses is used based on several macroeconomic indices such as the gross domestic product (GDP) and population. Based on the published earthquake loss data during 1980—1995, the relations between GDP and earthquake losses have been formulated empirically for several intensity ranges. The world’s land surface was divided into unit cells with 0.5°×0.5°in size, the GDP of each cell was apportioned based on its population and the GDP and population of the region to which it belongs. The predicted seismic loss of the cell was then estimated from the seismic展开更多
Some earthquakes in recent years (such as Tangshan earthquake (1976, China), North Ridge earthquake (1994, USA), Kobe earthquake (1995, Japan)) did not occur in known faults;moreover, the detailed data of geology, ear...Some earthquakes in recent years (such as Tangshan earthquake (1976, China), North Ridge earthquake (1994, USA), Kobe earthquake (1995, Japan)) did not occur in known faults;moreover, the detailed data of geology, earthquake, crust deformation, etc. needed by the fault model are very difficult to obtain in many regions of the world. A simplified method of global seismic hazard analysis is developed, based on an area source model and by using seismicity data, and the global seismic hazard map is compiled. To evaluate the effectiveness and credibility of the new method, comparison study of this map with the existing national maps has been performed, which implies that it is considerably valuable to apply this method to practical use.展开更多
基金supported by China Earthquake Administration under grants 200708008 and IES02092405
文摘Repeating microearthquakes were identified along the edge of the rupture area of the 2008 MW7.9 Wenchuan earthquake. Slip rates at depths derived from seismic moments and recurrence intervals are found to be systematically larger than those observed at surface. This large deep slip rate may explain the odds about the occurrence of this unanticipated event. Our observations here suggested that seismic hazard could be underestimated if surface measurements alone are employed.
基金supported by the National Natural Science Foundation of China(Grant Nos.42004041,42288201,and 91958209)。
文摘A shallow crustal velocity structure(above 10 km depth) is essential for understanding the crustal structures and deformation and assessing the exploration prospect of natural resources, and also provides priori information for imaging deeper crustal and mantle structure. Passive-source seismic methods are cost-effective and advantageous for regional-scale imaging of shallow crustal structures compared to active-source methods. Among these passive methods, techniques utilizing receiver function waveforms and/or body-wave amplitude ratios have recently gained prominence due to their relatively high spatial resolution. However, in basin regions, reverberations caused by near-surface unconsolidated sedimentary layers often introduce strong non-uniqueness and uncertainty, limiting the applicability of such methods. To address these challenges, we propose a two-step inversion method that uses multi-frequency P-RF waveforms and P-RF horizontal-to-vertical amplitude ratios. Synthetic tests indicate that our two-step inversion method can mitigate the non-uniqueness of the inversion and enhance the stability of the results. Applying this method to teleseismic data from a linear seismic array across the sedimentary basins in Northeast China, we obtain a high-resolution image of the shallow crustal S-wave velocity structure along the array. Our results reveal significant differences between the basins and mountains. The identification of low-velocity anomalies(<2.8 km s^(-1)) at depths less than 1.0 km beneath the Erlian Basin and less than 2.5 km beneath the Songliao Basin suggests the existence of sedimentary layers. Moreover, the high-velocity anomalies(~3.4–3.8 km s^(-1)) occurring at depths greater than 7 km in the Songliao Basin may reflect mafic intrusions emplaced during the Early Cretaceous. Velocity anomaly distribution in our imaging result is consistent with the location of the major faults, uplifts, and sedimentary depressions, as well as active-source seismic results. This application further validates the effectiveness of our method in constraining the depth-dependent characteristics of the S-wave velocity in basins with unconsolidated sedimentary cover.
文摘Most earthquake loss studies use an inventory approach by which the predicted damages in various categories of structures and facilities in a concerned region are estimated and added together to obtain the total estimated. Such an approach requires a detailed inventory database of the structures and facilities in the region, which is not always readily available in many regions of the world. Therefore, an alternative means of estimating earthquake losses is used based on several macroeconomic indices such as the gross domestic product (GDP) and population. Based on the published earthquake loss data during 1980—1995, the relations between GDP and earthquake losses have been formulated empirically for several intensity ranges. The world’s land surface was divided into unit cells with 0.5°×0.5°in size, the GDP of each cell was apportioned based on its population and the GDP and population of the region to which it belongs. The predicted seismic loss of the cell was then estimated from the seismic
文摘Some earthquakes in recent years (such as Tangshan earthquake (1976, China), North Ridge earthquake (1994, USA), Kobe earthquake (1995, Japan)) did not occur in known faults;moreover, the detailed data of geology, earthquake, crust deformation, etc. needed by the fault model are very difficult to obtain in many regions of the world. A simplified method of global seismic hazard analysis is developed, based on an area source model and by using seismicity data, and the global seismic hazard map is compiled. To evaluate the effectiveness and credibility of the new method, comparison study of this map with the existing national maps has been performed, which implies that it is considerably valuable to apply this method to practical use.
