Based on the studies of earthquake activity, tectonic movement, crustal shortening rate, fault activity, local stress field and historical characteristics of strong earthquake activities in Xinjiang, we divide the sou...Based on the studies of earthquake activity, tectonic movement, crustal shortening rate, fault activity, local stress field and historical characteristics of strong earthquake activities in Xinjiang, we divide the south part of Xinjiang into 4 seismotectonic zones, namely, the eastern segment of south Tianshan seismic belt, the Kalpin block, the Kashi-Wuqia junction zone, and the west Kunlun Mountains seismic belt. Using earthquake catalogues from Xinjiang since 1900, and on the basis of integrity analysis of earthquake records in different magnitude ranges, the seismicity state of different seismotectonic zones is analyzed quantificationaUy by calculating the mean value of annual strain energy release, annual rate of earthquakes with different lower limits of magnitude, b-value, and the parameter m of accelerating strain release model. The characteristic indexes of seismicity state for each of the seismic tectonic zones are then determined, which provide a quantitative basis for earthquake tendency analysis and judgment.展开更多
The Zhangjiakou-Bohai Sea fault zone located in the northern part of the North China region is a seismotectonic zone controlling the present-day strong earthquake activities. Under the effect of regional principal com...The Zhangjiakou-Bohai Sea fault zone located in the northern part of the North China region is a seismotectonic zone controlling the present-day strong earthquake activities. Under the effect of regional principal compressive stress with the direction of NEE-SWW, a series of NE-trending active tectonic zones have developed, which form a group of conjugated shear fracturing systems and control the occurrence of the present-day strong earthquakes. The feature of crustal deformation around this fault zone is studied in the paper. The long-term crustal deformation pattern from GPS measurements exhibits a relatively complete left-lateral strike-slip movement along the active fault zone. However, studies on crustal deformation by stages indicate that a series of NE-trending large-scale anomalous gradient zones have appeared along the Zhangjiakou-Bohai Sea fault zone before moderately strong earthquakes. They are represented respectively by the activities of the Tangshan-Hejian, the Sanhe-Laishui and the Yanhuai-Shanxi seismotectonic zones. This may indicate the occurrence of med-term precursors to moderately strong earthquakes along Zhangjiakou-Bohai Sea zone. The results in the paper show that the crustal deformation pattern before strong earthquake reveals the information of strain status in the deep seismogenic zone, while the chaotic pattern after the occurrence of strong earthquake represents the adjustment of the covering strata.展开更多
Jeddah-Makkah regionis have been suffering from earthquake crisis where some moderate to destructive earthquakes have been recorded. These earthquake activities are oriented along major faults or clustered in certain ...Jeddah-Makkah regionis have been suffering from earthquake crisis where some moderate to destructive earthquakes have been recorded. These earthquake activities are oriented along major faults or clustered in certain spots. Moreover, these earthquake events have annual recurrence periods, so the identification of these seismogenic source zones is of utmost importance for mapping the most hazardous localities which should be avoided in the future urban planning. Historical and instrumental earthquakes have been collected from national and international data centers and unified in catalogue. The existence of microearthquakes inland suggests that there is a significant level of tectonic activity at away from the axial trough of the Red Sea. Then, seismogenic source zones have been defined depending on the major tectonic trends; distribution of earthquake epicenters, seismicity rate（a ＆ b- values） and fault plane solution of major earthquakes. It is concluded that Jeddah-Makkah region is affected by the outlined five seismogenic source zones; three of these zones aligned of the main Red Sea axial trough（southwestern Jeddah, western Jeddah, and northwestern Jeddah zones）, while the other two zones are located in the land area of the region（Thewal-Rabegh and Jeddah-Makkah zones）. These inland zones correlated well with the main trends of major tectonics which refleet the reactivation of tectonic movements along these fault trends. The Red Sea zones are in agreement with the main path of the axial trough. The range of b-value in these identified zones is 0.65 to 1.03 through these identified zones. The area characterized by higher b-values could be indicative of a relative low stress regime which was a result of resulting from the stress release by the earthquakes. Whereas, the areas of lower b-values can be considered as an evidence of a relatively higher stress regime associated with a dominantly extensional stresses. Based on aforementioned, the region is suffering from different stress level accumulations which, in turn, cause earthquakes with different magnitudes. Accordingly, deployment of local seismograph network through Jeddah-Makkah region is highly recommended. These results will support, to a great extent, seismic hazard assessment and risk mitigation of the region.展开更多
基金supported by the Special Scientific Research Funds for Earthquake Studies, entitled "Development of Dynamic Evaluation System of Seismicity State in the Chinese Continent (Grant No. 200708020)"
文摘Based on the studies of earthquake activity, tectonic movement, crustal shortening rate, fault activity, local stress field and historical characteristics of strong earthquake activities in Xinjiang, we divide the south part of Xinjiang into 4 seismotectonic zones, namely, the eastern segment of south Tianshan seismic belt, the Kalpin block, the Kashi-Wuqia junction zone, and the west Kunlun Mountains seismic belt. Using earthquake catalogues from Xinjiang since 1900, and on the basis of integrity analysis of earthquake records in different magnitude ranges, the seismicity state of different seismotectonic zones is analyzed quantificationaUy by calculating the mean value of annual strain energy release, annual rate of earthquakes with different lower limits of magnitude, b-value, and the parameter m of accelerating strain release model. The characteristic indexes of seismicity state for each of the seismic tectonic zones are then determined, which provide a quantitative basis for earthquake tendency analysis and judgment.
文摘The Zhangjiakou-Bohai Sea fault zone located in the northern part of the North China region is a seismotectonic zone controlling the present-day strong earthquake activities. Under the effect of regional principal compressive stress with the direction of NEE-SWW, a series of NE-trending active tectonic zones have developed, which form a group of conjugated shear fracturing systems and control the occurrence of the present-day strong earthquakes. The feature of crustal deformation around this fault zone is studied in the paper. The long-term crustal deformation pattern from GPS measurements exhibits a relatively complete left-lateral strike-slip movement along the active fault zone. However, studies on crustal deformation by stages indicate that a series of NE-trending large-scale anomalous gradient zones have appeared along the Zhangjiakou-Bohai Sea fault zone before moderately strong earthquakes. They are represented respectively by the activities of the Tangshan-Hejian, the Sanhe-Laishui and the Yanhuai-Shanxi seismotectonic zones. This may indicate the occurrence of med-term precursors to moderately strong earthquakes along Zhangjiakou-Bohai Sea zone. The results in the paper show that the crustal deformation pattern before strong earthquake reveals the information of strain status in the deep seismogenic zone, while the chaotic pattern after the occurrence of strong earthquake represents the adjustment of the covering strata.
基金the Deanship of Scientific Research at King Saud University for its funding this research group (No. RG-1436-011)
文摘Jeddah-Makkah regionis have been suffering from earthquake crisis where some moderate to destructive earthquakes have been recorded. These earthquake activities are oriented along major faults or clustered in certain spots. Moreover, these earthquake events have annual recurrence periods, so the identification of these seismogenic source zones is of utmost importance for mapping the most hazardous localities which should be avoided in the future urban planning. Historical and instrumental earthquakes have been collected from national and international data centers and unified in catalogue. The existence of microearthquakes inland suggests that there is a significant level of tectonic activity at away from the axial trough of the Red Sea. Then, seismogenic source zones have been defined depending on the major tectonic trends; distribution of earthquake epicenters, seismicity rate（a ＆ b- values） and fault plane solution of major earthquakes. It is concluded that Jeddah-Makkah region is affected by the outlined five seismogenic source zones; three of these zones aligned of the main Red Sea axial trough（southwestern Jeddah, western Jeddah, and northwestern Jeddah zones）, while the other two zones are located in the land area of the region（Thewal-Rabegh and Jeddah-Makkah zones）. These inland zones correlated well with the main trends of major tectonics which refleet the reactivation of tectonic movements along these fault trends. The Red Sea zones are in agreement with the main path of the axial trough. The range of b-value in these identified zones is 0.65 to 1.03 through these identified zones. The area characterized by higher b-values could be indicative of a relative low stress regime which was a result of resulting from the stress release by the earthquakes. Whereas, the areas of lower b-values can be considered as an evidence of a relatively higher stress regime associated with a dominantly extensional stresses. Based on aforementioned, the region is suffering from different stress level accumulations which, in turn, cause earthquakes with different magnitudes. Accordingly, deployment of local seismograph network through Jeddah-Makkah region is highly recommended. These results will support, to a great extent, seismic hazard assessment and risk mitigation of the region.
