Review on study of seismotectonics in China

This paper reviews briefly the progresses made during the last four years (1999～2002) in study of seismotectonics in China, especially appraises the achievements in the fields of the crustal and upper mantle‘s structure, the active faults and tectonic setting of large earthquakes, the crustal deformation, and the numerical simulation. Most earth-quakes occurred in China belong to continental earthquakes. Therefore, Chinese seismologists pay more attention to the continental earthquakes. Based on improvements of the observation systems in China during the ninth Five-Year Plan, the studies on seismotectonics have achieved great progresses.     

Discussion on the feature of strong earthquake: Orderly distribution in time, space and intensity before the Western Kunlun Mountain Pass M=8.1 earthquake

Introduction The Western Kunlun Mountain Pass M=8.1 earthquake occurred on November 14, 2001 is the other M=8 earthquake occurred 50 years after Dangxiong, Tibet M=8.0 earthquake in Chinese mainland. The earthquake has caused the attention of the seismologists in the following aspects: 1) The fracture length is more than 400 km, which is far away from the estimated length by the statistic empirical function between the magnitude and the fracture length (WANG, et al, 2002); 2) The aftersh…     

New national seismic zoning map of China

1 Background of the new national seismic zoning map The policy of seismic disaster mitigation in the Chinese mainland is prevention first. According to the law, the earthquake design for ordinary structures must fit the demand of national seismic zoning map. Seismic zoning map is the basis of the earthquake design (TANG, 1998; WU, et al, 1998). The seismic zoning map must be updated with the progress in methodology and accumula-tion of the data. There are three generations of national seis…     

德令哈6．6级地震前地震活动及地震序列特征

德令哈6．6级地震发生在青海省地震局2003年度会商确定的应注意地区内，震前测震学出现多项中短期异常。该地震序列从其能量释放比、震级差均符合主震一余震型判断指标，为主震-余震型序列。序列跟踪工作总结出该序列早期阶段(20天内)预测强余震的几项指标。     

德令哈6．6级地震前卫星红外长波辐射OLR的分析

应用NOAA卫星资料反演的地震长波辐射值OLR对2003年4月17日发生在青海省德令哈西的6．6级地震进行了追踪研究。结果显示：2003年1月起OLR距平值出现明显的高值异常区域。     

石泉ML4．7级地震前天水深井水温的短临异常特征

分析了天水台数字深井水温资料在陕西石泉ML4．7级地震前的异常特征，发现在震前5天内深井水温发生大幅度的降升变化，呈负脉冲形态，表现为典型的脉冲型前兆异常形态特征。     

Seismicity anomalies before the great earthquake of M_S=8.1 in the Kunlun Pass and its significance to earthquake prediction

Introduction The MS=8.1 earthquake occurred in west of the Kunlun Pass on November 14, 2001. It is the greatest earthquake occurred in China since the last half of the century and is an important event in recent seismic history of China. Some specialists consider that the earthquake occurred in the area where the earthquake monitoring capability is lowest in Chinese mainland; no striking precursory seismicity was found. The study on the precursory seismicity before the earthquake has not b…     

Re-appraisal of seismicity and seismotectonics in the north-eastern Algeria Part II: 20th century seismicity and seismotectonics analysis

The main objective of the research work isthe homogenisation of the two recentAlgerian earthquake catalogues for thecommon covered period of time, from 1900 to1990, for the region under considerationlimited by [33^°N–38^°N,4^°E-9.5^°E] and the updatingof the catalogue for the twentieth century(1900–2000). To mitigate the deficiencyof the incompleteness of catalogue, aneffort was made to establish a correlationbetween surface-wave magnitude Ms andbody-wave magnitude m_b in the form ofMs = a + b (m_b). A complete, exact andhomogeneous earthquake catalogue as much aspossible, comprising 870 seismic events,has been compiled. Seismicity analysis ofthe region shows a strong concentration ofseismicity along a band of no more than400 km width oriented mainly in theeast-west direction parallel to the coast.Moreover, earthquakes in this zone arerather associated to strike-slip mechanism.The focal mechanism show a regional stressregime that corresponds to horizontalcompression in NW-SE to N-S direction. As aresult of the review of the seismicity ofnorth-eastern Algeria from the compilationof checked and corrected data and itscorrelation with other geologic andgeophysical investigations based ondocumentary sources, it was possible toconstruct a most complete seismotectonicmap. It leads also to delineate fourseismogenic zones in the Tellian Atlas, aless important zone in the Saharan Atlas, asixth zone at the boundary of both Atlasand finally, a seventh one along thecoastal zone. The seismicity-active faultscorrelation of some of these defined zonesis examined in details with a specialattention to the Saharan Atlas zone, theHodna and Biban zone as well as Soummam andBabor zone where further research workallowed to find some neotectonic featuresconsidered as a significant sign of recenttectonic activity.     

An Mw based earthquake Catalogue for central, northern and northwestern Europe using a hierarchy of magnitude conversions

Data from 25 local catalogues and 30special studies of earthquakes in central,northern and northwestern Europe have beenincorporated into a Databank. The dataprocessing includes discriminating eventtypes, eliminating fake events and dupletsand converting different magnitudes andintensities to M_w if this is not givenby the original source. The magnitudeconversion is a key task of the study andimplies establishment of regressionequations where no local relations exist.The Catalogue contains tectonic events fromthe Databank within the area44°N–72°N,25°W–32°E and the time period1300–1993. The lower magnitude level forthe Catalogue entries is setat M_w == 3.50. The area covered by thedifferent catalogues are associated withpolygons. Within each polygon only datafrom one or a small number of the localcatalogues, supplemented by data fromspecial studies, enter the Catalogue. Ifthere are two or more such catalogues orstudies providing a solution for an event,a priority algorithm selects one entry forthe Catalogue. Then M_w is calculatedfrom one of the magnitude types, or frommacroseismic data, given by the selectedentry according to another priority scheme.The origin time, location, M_w magnitude and reference are specified for eachentry of the Catalogue. So is theepicentral intensity, I₀, if providedby the original source. Following thesecriteria, a total of about 5,000earthquakes constitute the Catalogue.Although originally derived for the purposeof seismic hazard calculation within GSHAP,the Catalogue provides a data base for manytypes of seismicity and seismic hazardstudies.     

Exploration and Study on Deep Crust Structural Characteristics in the Jiashi-Artux Seismic Region

The data from two deep seismic sounding profiles was processed and studied comprehensively. The results show that crnst-mantle structures in the investigated region obviously display layered characteristics and velocity structures and tectonic features have larger distinction in different geological structure blocks. The boundary interface C between the upper and lower crust and Moho fluctuate greatly. The shallowest depths of C (30.0km) and Moho (45.5km) under Jiashi deepen sharply from Jiashi to the western Kunlun mountain areas, where the depths of C and Moho are 44.0km and 70.0km, respectively. The higher velocity structures in the Tarim massif determine its relatively “stable“ characteristics in crust tectonics. The phenomenon in the Jiashi region, where the distribution of earthquake foci mostly range from 20kin to 40kin in depth, may infer that the local uplift of C and Moho interface, anomalonsly lower velocity bodies and deep large faults control earthquake occurrence and seismogenic processes in the Jiashi strong earthquake swarm.