Preliminary analysis on the tectonic stress level in the source region of Tangshan earthquake

Introduction Analyzing tectonic stress field based on focal mechanism data is an important way to the study tectonic evolvement of lithosphere and associated dynamic process. Such studies growrapidly in China and abroad (Zoback, 1992; Plenefisch, Bonjer, 1997; XU, 1985; CUI, XIE, 1999). At present most of the studies focus on the inversion of focal mechanism data for the direction and relative magnitude of stress tensor, and few on absolute stress. Using focal mechanism and fault scratch,…     

The environment shear stress field for the 1976 Tangshan earthquake sequence

（陈培善，肖磊，白彤霞，王溪莉）Ｔｈｅｅｎｖｉｒｏｎｍｅｎｔｓｈｅａｒｓｔｒｅｓｓｆｉｅｌｄｆｏｒｔｈｅ１９７６Ｔａｎｇｓｈａｎｅａｒｔｈｑｕａｋｅｓｅｑｕｅｎｃｅ￥Ｐｅｉ－ＳｈａｎＣＨＥＮ；ＬｅｉＸＩＡＯ；Ｔｏｎｇ－ＸｉａＢＡＩａｎｄＸｉ－ＬｉＷＡ...     

A source extent analysis of the Lancang earthquake(M_s=7.6)of 1988

ＡｓｏｕｒｃｅｅｘｔｅｎｔａｎａｌｙｓｉｓｏｆｔｈｅＬａｎｃａｎｇｅａｒｔｈｑｕａｋｅ（Ｍｓ＝７．６）ｏｆ１９８８ＳＩ－ＨＵＡＺＨＥＮＧ（郑斯华）ＪＩＡＮＹＡＮＧ（杨健）ＣｅｎｔｅｒｆｏｒＡｎａｌｙｓｉｓａｎｄｐｒｅｄｉｃｔｉｏｎ,ＣｈｉｎａＳｅｉｓ...     

In search of potential earthquake source regions in the Chinese mainland in the light of ambient shear stress field

ＩｎｓｅａｒｃｈｏｆｐｏｔｅｎｔｉａｌａｒｔｈｑｕａｋｅｓｏｕｒｃｅｒｅｇｉｏｎｓｉｎｔｈｅＣｈｉｎｅｓｅｍａｉｎｌａｎｄｉｎｔｈｅｌｉｇｈｔｏｆａｍｂｉｅｎｔ　ｓｈｅａｒｓｔｒｅｓｓｆｉｅｌｄＰｅｉ－ＳｈａｎＣＨＥＮ；（陈培善）Ｔｏｎｇ－ＸｉａＢＡ...     

Variation of stress field in the source region around a strong shock：an example

Ｖａｒｉａｔｉｏｎｏｆｓｔｒｅｓｓｆｉｅｌｄｉｎｔｈｅｓｏｕｒｃｅｒｅｇｉｏｎａｒｏｕｎｄａｓｔｒｏｎｇｓｈｏｃｋ：ａｎｅｘａｍｐｌｅＧｕｔ－ＬｉｎｇＤＩＡＯ（刁桂苓），Ｌｉ－ＭｉｎＹＵ（于利民）ａｎｄＱｉｎ－ＺｕＬＩ（李钦祖）（Ｓｅｉｓｍｏｌｏｇｉ...     

The anomalous reactions of the geomagnetic horizontal field transfer functions before Tangshan earthquake

ＴｈｅａｎｏｍａｌｏｕｓｒｅａｃｔｉｏｎｓｏｆｔｈｅｇｅｏｍａｇｎｅｔｉｃｈｏｒｉｚｏｎｔａｌｆｉｅｌｄｔｒａｎｓｆｅｒｆｕｎｃｔｉｏｎｓｂｅｆｏｒｅＴａｎｇｓｈａｎｅａｒｔｈｑｕａｋｅＳＨＡＯＪＩＮＧＧＯＮＧ（龚绍京）ＨＵＡＲＡＮＣＨＥＮ（...     

Characteristics of teh seismic source stress field in teh joint region of Xianshuihe ,Long Monitoring the horizontal movement along the Shanxi faults

Twenty-two earthquakes (M _L=2.2–3.7) in the joint region of Xianshuihe, Longmenshan and An’ninghe faults are studied in this paper. The source mechanism solutions of these events are obtained using P-wave first motion method, and the characteristics of the source stress field and rupture in the joint region are summarized preliminarily with some results of other researchers. Being strongly extruded by the approximately horizontal regional stress with the direction from north-west to south-east and the effect of the complex tectonics in the region, the source stress field has complex and variable characteristics. The earthquakes mainly show normal or strike-slip faults in Yajiang, North-triangle and west of Chengdu-block areas, indicating that the vertical forces have been playing an important role in the source stress fields, while the earthquakes mainly show reverse or strike-slip faults in Baoxing-Tianquan area, with the horizontal components of the principal pressure stress axes identical to the south-west direction to which the shallow mass is moving. We think that the manifold combinations of earthquake faults are the micro-mechanism based upon which the large regional shallow crust mass has been moving continually.     

Spatial and temporal variation of gravity field in the capital region

Ｓｐａｔｉａｌａｎｄｔｅｍｐｏｒａｌｖａｒｉａｔｉｏｎｏｆ　ｇｒａｖｉｔｙ　ｆｉｅｌｄｉｎｔｈｅｃａｐｉｔａｌｒｅｇｉｏｎＣｈａｎｇ－ＣａｉＨＵＡ；（华昌才）ＹｏｎｇＧＵＯ；（果勇）Ｄｕａｎ－ＦａＬＩＵ；（刘瑞法）ＧａｎｇＸＩＡＯ；（肖钢），Ｊ．Ｔ．...     

Statistical analysis on energy field of seismicity in Ningxia and its neighborhood region

IntroductionOneofnotablefeaturesofseismicityistherandomoccurrenceofearthquakesinspaceandtime.Oneessentialelementofseismicityisthatearthquakereleasedenergycanbetakenastherandomfunctionsofspatialandtemporalcoordinates.Therandomfunctioncanbecalledseismicityenergystochasticfieldorearthquakeenergyfield.Sincetheseismicityisrelatedinspaceandtime,usingtheconceptofstochasticfield,thetotalfeatureofregionalseismicactivitycanbeconsidered,ratherthanthestatisticsofasingleearthquakeinthepast.Therefore,thefe…     

The mechanism of regional gravity changes before and after the Tangshan earthquake

ＴｈｅｍｅｃｈａｎｉｓｍｏｆｒｅｇｉｏｎａｌｇｒａｖｉｔｙｃｈａｎｇｅｓｂｅｆｏｒｅａｎｄａｆｔｅｒｔｈｅＴａｎｇｓｈａｎｅａｒｔｈｑｕａｋｅＲＵＩ－ＨＡＯＬＩ（李瑞浩）ＪＩＡＮ－ＬＩＡＮＧＨＵＡＮＧ（黄建梁）ＨＵＩＬＩ（李辉）ＤＯＮＧ－ＳＨＥＮＧ...     

2016年8月唐山震群视应力变化特征

2016年8月河北唐山发生震群活动,具有频次高、持续时间长等特点。利用首都圈数字化地震台网监测的2016年1月—2017年5月河北唐山地区M_L≥2.5地震,采用遗传算法反演震源参数,计算相应地震视应力值。分析结果如下：①此次地震序列为前震—主震—余震型;②视应力值在震群发生前明显增高,发生过程中出现高低相间现象,在M_L 4.3主震出现峰值,震源区应力状态不稳定,震后视应力恢复正常;③震群视应力与震级呈现一定正相关。     

1992兰德斯地震震源处应力量值的研究

给出了根据地震前后应力轴偏转、地震应力降和地震前后相对主应力大小,计算震源处应力量值的方法.并将该方法运用于兰德斯地震的霍姆斯特德谷断层段,获得了该子断层10 km深度处震前最大、中间和最小主应力的量值分别为271,266 MPa和259 MPa;震前断层面上的正应力和剪切应力分别为265MPa和6.2 MPa;震后断...     

Visco-elastic stress triggering model of Tangshan earthquake sequence

We calculated the Coulomb failure stress change generated by the 1976 Tangshan earthquake that is projected onto the fault planes and slip directions of large subsequent aftershocks.Results of previous studies on the seismic fail-ure distribution,crustal velocity and viscosity structures of the Tangshan earthquake are used as model constraints.Effects of the local pore fluid pressure and impact of soft medium near the fault are also considered.Our result shows that the subsequent Luanxian and Ninghe earthquakes occurred in the regions with a positive Coulomb fail-ure stress produced by the Tangshan earthquake.To study the triggering effect of the Tangshan,Luanxian,and Ninghe earthquakes on the follow-up small earthquakes,we first evaluate the possible focal mechanisms of small earthquakes according to the regional stress field and co-seismic slip distributions derived from previous studies,assuming the amplitude of regional tectonic stress as 10 MPa.By projecting the stress changes generated by the above three earthquakes onto the possible fault planes and slip directions of small earthquakes,we find that the "butterfly" distribution pattern of increased Coulomb failure stress is consistent with the spatial distribution of follow-up earthquakes,and 95% of the aftershocks occurred in regions where Coulomb failure stresses increase,indicating that the former large earthquakes modulated occurrences of follow-up earthquakes in the Tangshan earthquake sequence.This result has some significance in rapid assessment of aftershock hazard after a large earthquake.If detailed failure distribution,seismogenic fault in the focal area and their slip features can be rapidly determined after a large earthquake,our algorithm can be used to predict the locations of large aftershocks.     

Focal mechanisms and tectonic stress field of the Xinfengjiang earthquake

Altogether 83 events were recorded clearly by all the 8 sub-seismometric stations of the telemetrered seismic network in the Xinfengjiang area during the period from October 1st 1983 to April 30th 1987. Based upon the difference of the initial motion of P waves, the authors divided the 83 earthquakes into 37 pattens. Combining similar pattens, we have got 5 types of focal mechanism solutions. The recent tectonic stress field of the Xinfengjiang region is discussed. The characteristics of the stress axis and the nodal planes are different from which our predecessors got earlier; but the present results is similar to which put forward by the authors in 1981. This paper shows that the tectonic stress field is clearly characterized by a compression in the N-S direction. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica 13. 462–476, 1991.     

A possible change in stress field orientation due to the 1976 Tangshan earthquake

Two techniques are used to study the stress field in the Tangshan region. First, the mean directions of principal stress axes in three subregions of the Tangshan aftershock region are determined from 29 focal mechanism solutions. In doing so a slip-fitting technique is applied which determines the mean stress tensor by minimizing the angle between the observed slip direction on every fault plane and the calculated shear stress resolved onto the fault planes. Each of the two nodal planes of the focal mechanism solutions are alternately considered as a possible fault plane. Second, by making a grid search over all possible orientations of stress axes, the meanP,B andT axes in the Tangshan region, both before and after the Tangshan mainshock, are found on the basis of firstP-wave polarity readings from a number of small earthquakes. The results indicate that there is a possible azimuthal change of the principal stress axes in the focal region due to the occurrence of the mainshock.     

云南耿马7.2级地震破裂与震源应力场

1 98 8年 1 1月 6日在云南省澜沧县和耿马县境内先后发生了 7.6级和 7.2级强烈地震。其中 7.2级地震在震中区小黑江两岸灰岩裸露区出现了具有构造意义的地裂缝带。采用断层滑动矢量法反演出形成上述地裂缝带的应力张量为 :σ1走向 2 2 3°,倾角 2 8°;σ2 走向 42°,倾角6 2°;σ3 走向 1 3 3°,倾角 0°;应力比 R=0 .5 7,总体显示出走滑兼压性特征 ,基本代表了震源机制解所反映的震源应力场特征。断面滑动矢量解析可做为一种判定地裂缝是否是构造成因的方法     

2003年6月青岛震群地震震源机制与震源区应力场特征

利用山东数字地震台网记录的2003年6月青岛震群波形资料,由P波、SV波、SH波初动和它们之间的振幅比,联合计算了ML≥2.9地震的震源机制解。结果表明,震群发生前期,震源机制较为一致,P轴与北东东(80°)近水平方向的区域应力场主压应力方向一致,震群发生后期震源机制变化相对较大。上述现象相对于强震P轴方向与区域应力场主压应力方向一致,而余震P轴絮乱的现象有一定的相似性。但相对于强震在震后引起的主压应力方向变化(约40°~96°)来说,青岛震群地震引起震源区P轴的变化(约45°)并不显著。     

隆昌及邻近区域小震群分析

本文根据主要地震震源机制、震源深度以及序列参数,对最近2年发生在四川省隆昌地区的3次4级以上地震序列进行了对比分析。基于区域地震活动特征、序列特征及地震视应力计算结果,对区域地震危险性进行了初步分析。