天津及邻区1999～2000年地震震源机制研究

文中使用的是天津市、河北省地震台的 P,Pn波初动方向资料 ,研究了 1 999～ 2 0 0 0年发生在天津及邻区的 4个地震的震源机制。其中 1 999年 8月 1 1日河北省大城县 ML 3.1地震发生在大城断裂上 ,震源机制解的节面 (走向 2 0 8°,倾角 54°,滑动角 1 2°)与大城断裂的走向一致。2 0 0 0年 1月 2 6日蓟县 ML 3.3地震发生在蓟县 -邦均断裂上 ,震源机制解的节面 (走向 2 85°,倾角 77°,滑动角 1 38°)与蓟县 -邦均断裂的走向一致。表明这两个断层在活动 ,这两个地震发生在多年来 (有感 )地震不多的地区 ,并且是发生在首都圈中部 ,应该引起注意     

The earthquake sequence of May 1951 at Jucuapa, El Salvador

Three earthquakes that happened over two days in May 1951 caused extensive damage to villages in a small area of eastern El Salvador (Central America). Contemporary hypocentral solutions indicated focal depths, confirmed by re-calculations using available seismic data, of the order of 90 km, suggesting events associated with the subducted Cocos plate. Macroseismic observations strongly indicate that the earthquakes were of very shallow focus and this is supported by wave-form modeling and the appearance of seismograms recorded in Guatemala. A re-evaluation of the location and source characteristics for these events is presented, together with a fault plane solution and additional macroseismic evidence. The implications for seismic hazard and risk assessment in Central America, where shallow earthquakes of moderate magnitude, frequently occurring in clusters, pose the greatest threat to settlements which, like the area affected by these events, are concentrated along the axis of Quaternary volcanoes.     

A discussion on the amplitude ratios of PP and P waves for earthquakes with different focal mechanisms

Using the WKBJ approximation method we calculate the synthetic teleseismograms of P and PP waves to match the observed ones of six large Chinese earthquakes with known focal mechanisms: Tibet earthquake of July 14, 1973; Haicheng earthquake of February 4, 1975; Songpan earthquakes of August 16, 1976, August 21, 1976 and August 23, 1976 and Nignhe earthquake of November 15, 1976. The focal mechanism of the Tibet earthquake is discussed to examine the technique used in the calculation. We note that the amplitude ratios of PP and P waves (A _PP/A _P) have different characteristics for dip—slip events and strike—slip events within certain epicentral distances. We calculate the synthetic teleseismograms of P and PP waves for the strike—slip and dip—slip events with fault angles of 330°, 240° and 0°, focal depths of 8 km, 17 km and 24 km, at the assumed station with an azimuth of 310° and epicentral distances from 40°; to 80°. The diagrams of maximum amplitude ratios of PP and P waves (A _PP/A _P) versus distances are given. The possibility to use the (A _PP/A _P) values to give an approximate estimation for the focal mechanism type is discussed. This work may be useful for determining the focal mechanism type for those earthquakes which have only few records such as the Chinese earthquakes from the 1930s to 1960s. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 150–160, 1991.     

A tectonic stress map of China and adjacent regions from earthquakes occurred during 2000～2004

Earthquake focal mechanism solutions provide the basic information about the present-day regional tectonics stress distribution, which controls the activities of crustal faults. Therefore, continued efforts for updating the da-tabase of earthquake focal mechanism solutions are quite valuable and important. The international lithosphere program initiated the ″world stress map project″ (Zoback, 1992) since 1980′s. During this project, worldwide studies and measurements of present-day regional…     

Inversion of source process and related studies of the Taiwan Strait earthquake using genetic algorithm

Applying genetic algorithm to inversion of seismic moment tensor solution and using the data of P waveform from digital network and initial motion directions of P waves of Taiwan network stations, we studied the moment tensor solutions and focal parameters of the earthquake of M=7.3 on 16 September of 1994 in Taiwan Strait and other four quakes of M _L≥5.8 in the near region (21°–26°N, 115°–120°E). Among the five earthquakes, the quake of M=7.3 on September 16, 1994 in Taiwan Strait is the strongest one in the southeastern coast area since Nan’ao earthquake of M=7.3 in 1918. The results show that moment tensor solution of M=7.3 earthquake is mainly double-couple component, and is normal fault whose fault plane is near NW. The strike of the fault plane resembles that of the distributive bands of earthquakes before the main event and fracture pattern shown by aftershocks. The tension stress axis of focal mechanism is about horizontal, near in NE strike, the compressive stress axis is approximately vertical, near in NWW strike. It seems that this quake is controlled by the force of Philippine plate’s pressing Eurasian plate in NW direction. But from the viewpoint of P axis of near vertical and T axis of near horizontal, it is a normal fault of strong tensibility. There are relatively big difference between focal mechanism solution of this quake and those of the four other strong quakes. The complexity of source mechanism solution of these quakes represents the complexity of the process of the strait earthquake sequences. Contribution No. 98A01001, Institute of Geophysics, State Seismological Bureau, China. The subject is supported and helped by Academician Yun-Tai CHEN, Profs. Qing-Yao HONG, Zhen-Xing YAO, Tian-Yu ZHENG, Yao-Lin SHI, Ji-An XU, Bo-Shou HUANG and colleague Mei-Jian AN, Xue-Reng DING, Rui-Feng LIU. De-Chong ZHANG and Ming Li provided the digital data warm-heartedly. Lin-Ying WANG offered us the catalogue of earthquakes in southeastern coastal area in China. Xi-Li WANG and Tong-Xia BAI provided us the issued annual reports data. The authors would like to express their gratitude to all of these people. This paper is sponsored by the National Natural Science Foundation of China and Scientific and Technological Commission of Shantou, Guangdong Province.     

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Applying artificial neural networks to achieve quantitative division of potential focal regions

（姜效典，张维岗）Ａｐｐｌｙｉｎｇａｒｔｉｆｉｃｉａｌｎｅｕｒａｌｎｅｔｗｏｒｋｓｔｏａｃｈｉｅｖｅｑｕａｎｔｉｔａｔｉｖｅｄｉｖｉｓｉｏｎｏｆｐｏｔｅｎｔｉａｌｆｏｃａｌｒｅｇｉｏｎｓ￥Ｘｉａｏ－ＤｉａｎＪＩＡＮＧａｎｄＷｅｉ－ＧａｎｇＺＨＡＮＧ（...     

大同地震序列的震源机制解

使用ＣＤＳＮ长周期地震波形记录，利用Ｈｅｌｍｂｅｒｇｅｒ（１９６８）的广义地震射线理论得到的线性反演地震矩张量的方法，对１９８９年１０月１８日－１９９１年３月２５日发生在大同的４个Ｍｓ＞５．０的地震进行了反演，计算了这些地震矩张量和断层面解。