中国甘肃张掖地区微震震源参数和震源特征

本文处理了张掖地区数字微震监测台网资料,求得了小震的震源参数,对中小地震相对比较集中的肃南地区部分地震进行了谱分析,估计了震源的谱参数。用振幅比方法反演了肃南地区小震的震源机制解及错动参数,分析了它们的构造意义和预报意义。     

长江三峡及周缘的小震震源参数

本文利用地震P波波谱测定了长江三峡及周缘地区介质的品质因子Q值和震源参数。该区Q值约在40-80之间,平均应力降约7.4bar,属低Q值、低应力降地区,为长江中下游地区地壳介质存在的低Q值普遍现象提供了又一佐证。本文同时讨论了该区各震源参数间的经验关系。     

巧家、石棉的小震震源参数的测定及其地震危险性的估计

根据巧家、石棉的小地震的观测资料,指出P波初动半周期在震级比较小时几乎是恒定的,在震级比较大时随震级的增大而增大;并指出P波初动振幅的对数也随震级的增大而增大。以圆盘形均匀位错面作为中、小地震震源的理论模式,计算了它所辐射的地震波远场位移,从而导出了体波初动半周期及振幅与震源尺度及波速等物理量的定量关系,解释了P波初动半周期及振幅与震级之间的经验关系。考虑到波在介质中的衰减和频散、地表面的影响以及地震仪器的频率特性,通过褶积方法合成了上述位错源产生的理论地震图,提出了直接由实际地震图上的初动半周期及振幅测定震源尺度、地震矩、应力降和错距等震源参数以及介质的晶质因数Q的方法.运用上述方法,测定了巧家、石棉两地区介质的品质因数Q和小震的震源参数.这两个地区介质的品质因数Q分别为620和560.石棉地区小地震的应力降大约在2-30巴之间,巧家地区小地震的应力降比较接近,平均约1.4巴.将这个结果和1962年3月19日新丰江地震与1975年2月4日海城地震的前、主震的应力降作对比,我们看到,巧家地区小震的应力降的特征与上述两次大地震的前震的应力降的特征是类似的,因此不能排斥巧家地区的小震是一个较大地震的前震的可能性.以测得的小震应力降的平均值（约1.4巴）作为这个可能发生的较大地震应力降的下限估计值,从主震震级和主震应力降的经验关系可以推知,其震级的下限是5.2级.     

天津地区小震应力状况

本文测定了天津地区1985—1990.9年间M_L=3.0以下小震的震源参数,共125次。结果表明:地震应力降△σ一般都不高,多数低于1.3Mpa;区域剪切应力和地震应力降均有明显的增高趋势。1989年末开始下降。由P波测定的介质Q值蓟县平均为350,宝坻、宁河、静海为250,天津西稍高。小震平均震源机制主压应力轴由北西9°,向西偏转26°。这些变化,不仅反应本地区应力调整过程,而且是华北区域应力变化过程的局部显示。     

京津地区Q值及平均应力降的分布特征

本文用P波初动半振幅和半周期直接测定介质的品质因素（Q值）和小震震源参数的方法,测定了京津地区十个区两个时间段介质的平均品质因数及小震震源参数。结果表明:唐山大震前在平谷台到唐山震区的路径上平均Q值明显的高,大约是其它区的一至二倍,并且唐山震区平均应力降最大,比其它区约大一个数量级,这说明唐山大震前这个地区介质的强度较高,整体性较强,并比其它地区积累了较高的应力。在这个基础上,对京津地区的地震趋势提出了看法。 此外,本文还给出了京津地区中小地震震源参数间的经验关系。     

用小震应力降估算滇西地区深部绝对应力值

本文用小震应力降估算了滇西地区5～8公里深的水平应力绝对值,并和剑川、下关地区的水压致裂结果进行了对比,发现两者是可以相比的。估算水平应力值随深度的增加而增加,线性相关的可信度较高。结果表明,由应力降估算绝对应力值是一种可行的办法,关键在于应力降结果的可靠性及震源定位精度的提高。     

肃南5.7级地震过程剪切波分裂特征

剪切波分裂应用于地震预报中的３个主要困难是：（１）如何自动定量识别剪切波快慢波到时；（２）用以认识其基本特征的震例太少；（３）因各次地震的复杂性，对所给剪切波分裂结果难以给出恰当的解释，本文研究了１９８８年１１月２２日甘肃肃南５．７级地震过程剪切波分裂的特征。所用资料为１９８８年８月到１９９０年８月中法合作张掖数字台网的记录。通过对张掖～肃南地区地壳结构模型的研究，确认了所用各次地震的真实出射角基     

1982年卢龙地震前后的小震震源参数

1982年10月19日,在唐山余震区的东北端卢龙,发生了一次ML=6.2(按北京电信传输台网的目录)的地震(3957'N,11904'E).为了监视卢龙地震前后小震震源参数的变化,本文考察了唐山-卢龙地区自1980年1月至1984年6月的情况.利用P波初动半周期,测定了160次ML=2.7——4.3的地震的震源参数.在所研究的震级范围内,初动半周期和震源半径不随ML而增大,应力降则随ML而增大.应力降的数值在0.1——50MPa的范围内变化,且主要集中在1MPa和5MPa之间.因此本文认为,对此地区,5MPa以上为高应力降,1MPa.以下为低应力降.该地区地震的空间分布表明,高应力降事件与随后发生的ML5的地震有明显的关系.在卢龙地震前一年多里,整个地区内的高应力降事件减少,低应力降事件增多;但在卢龙地震的震中附近发生了两次高应力降事件.      

温州珊溪水库ML3.9震群震源参数特征

采用地震波谱方法测定了温州珊溪水库地震序列的震源参数，分析了震源应力降特征及地震矩与震级的关系。研究结果认为：珊溪震群地震矩和震级统计关系为logMo=1．07ML 10．3；占地震总数60％的小震应力降为0．018～O．049MPa，珊溪震群属于低应力背景下的地震活动；珊溪震区应力降分维数D=0．85，属于低值，反映了震区介质强度和应力分布的非均匀程度较高。     

大同地震前后介质Q值和小震震源参数的变化

本文使用北京台网微机数字记录,通过波谱分析研究了大同地震前后介质Q值和小震应力降的变化。研究结果表明:(1)大同地震发生在低Q值区,震前Q值升高,震后恢复正常。(2)大同地震前,小震应力降明显升高,震后恢复正常,震前震后应力降的变化与介质Q值变化和应力变化有关。(3)大同地震前后小震震源参数确实有明显不同,无论是应力降、平均位错还是震源尺度都有明显不同。(4)大同地震前后小震波谱有明显变化。     

Study of theQ-value in and around Minle Basin

The digital seimograph network set up by China and France in Zhangye of China had been operated in 1988. The Zhangye network is situated in the middle segment of Hexi corridor and Qilina mountain, which was regarded as a monitoring earthquake area. Using the records of Zhangye digital network theQ-values in and around Minle basin have been measured. The results of this study showed that theQp-values range from 500 to 780, andQs-values range from 230 to 460. TheQ-values of inside of Minle basin are higher than that around the basin. The greater parts of moderate and strong earthquakes occurred along tectonic belts around the Minle basin. Moreover, TheQ-values increased with the depth of penctration of wave ray. The attenuation of S wave is stronger than P wave in shallow layer of crust. Some problems ofQ-value change versus time before and after Sunan eathquake (M _s=5.7) have been also disscussed. These results can be applied to study and to monitor seismic danger of the Minle monitoring area.     

Study of the Q -value in and around Minle Basin

The digital seimograph network set up by China and France in Zhangye of China had been operated in 1988. The Zhangye network is situated in the middle segment of Hexi corridor and Qilina mountain, which was regarded as a monitoring earthquake area. Using the records of Zhangye digital network theQ-values in and around Minle basin have been measured. The results of this study showed that theQp-values range from 500 to 780, andQs-values range from 230 to 460. TheQ-values of inside of Minle basin are higher than that around the basin. The greater parts of moderate and strong earthquakes occurred along tectonic belts around the Minle basin. Moreover, TheQ-values increased with the depth of penctration of wave ray. The attenuation of S wave is stronger than P wave in shallow layer of crust. Some problems ofQ-value change versus time before and after Sunan eathquake (M _s=5.7) have been also disscussed. These results can be applied to study and to monitor seismic danger of the Minle monitoring area. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 296–302, 1993.     

2006年11月23日新疆乌苏5.1级地震及部分地震学前兆异常特征

介绍了2006年11月23日新疆乌苏5.1级地震的基本参数、震源机制解、地震序列特征、发震构造和局部构造应力场;分析了震前数字地震波参数的变化和部分地震学前兆异常特征。研究结果认为,乌苏5.1级地震是博罗科努-阿齐克库都克断裂发生右旋走滑错动所致。震前观察到震中附近P波初动半周期、P波与S波振幅比以及应力降的变化。震前震中附近曾出现4级地震集中分布、3级地震空区图像,震前6~9个月出现震群活动,震前2个月温泉地震窗异常。除上述异常外,乌苏5.1级地震前整体异常比例不高。     

张北地震序列波谱分析

采用石家庄遥测台网数字化的地震记录,选取了1998年1月～1999年12月张北震区的146条地震,分别对P波、S波作了波谱分析,求取了拐角频率、地震矩、震源半径、应力降、平均位错和波谱能量。分析了拐角频率和应力降随时间的变化趋势,并讨论了震源参数相互之间的关系。结果表明,在1999年3月11日5．6级地震之前应力降和拐角频率均出现异常,同时发现,S波对环境的变化比P波敏感,P波较稳定,且各震源参数与震级有一定相关。     

2001年四川雅江6级地震的前震与余震震源参数的变化h

研究了2001年2月四川省雅江县发生的MS5.0前震、MS6.0主震及序列地震的震源机制、波谱参数及应力降的变化过程与震区地震活动．根据雅江地震的震源机制解，并结合余震空间分布图象分析，选雅江5.0级的节面Ⅰ为推测的地震断层，走向NNE；选雅江6.0级地震的节面Ⅱ为推测的地震断层，走向WNW，分析前震与主震的断层面走向是斜交的．雅江6.0级地震发生前震区应力降水平有所增加，这一现象与震区地震活动的增加是一致的．雅江地震序列的衰减起伏过程, 前、余震波谱变化, 以及震源力学错动机制等均呈现复杂特征．      

Inversion of multicomponent seismic time shifts for reservoir pressure and length: a feasibility study

Pressure drops associated with reservoir production generate excess stress and strain that cause travel‐time shifts of reflected waves. Here, we invert time shifts of P‐, S‐, and PS‐waves measured between baseline and monitor surveys for pressure reduction and reservoir length. The inversion results can be used to estimate compaction‐induced stress and strain changes around the reservoir. We implement a hybrid inversion algorithm that incorporates elements of gradient, global/genetic, and nearest neighbour methods and permits exploration of the parameter space while simultaneously following local misfit gradients. Our synthetic examples indicate that optimal estimates of reservoir pressure from P‐wave data can be obtained using the reflections from the reservoir top. For S‐waves, time shifts from the top of the reservoir can be accurately inverted for pressure if the noise level is low. However, if noise contamination is significant, it is preferable to use S‐wave data (or combined shifts of all three modes) from reflectors beneath the reservoir. Joint wave type inversions demonstrate improvements over any single pure mode. Reservoir length can be estimated using the time shifts of any mode from the reservoir top or deeper reflectors. We also evaluate the differences between the actual strain field and those corresponding to the best‐case inversion results obtained using P‐ and S‐wave data. Another series of tests addresses the inversion of the time shifts for the pressure drops in two‐compartment reservoirs, as well as for the associated strain field. Numerical testing shows that a potentially serious source of error in the inversion is a distortion in the strain‐sensitivity coefficients, which govern the magnitude of stiffness changes. This feasibility study suggests which wave types and reflector locations may provide the most accurate estimates of reservoir parameters from compaction‐induced time shifts.     

地震应力降与岩石破裂应力降

从应力降的静态理论,讨论了地震应力降的精度,并利用野外观测的最大位移和由地震波得到的地震矩,分别计算了十个研究较充分的地震应力降.对不同作者的结果作了比较,可以看出,应力降有因子为2的变化范围.但从统计观点看,地震应力降是分布在几巴到几百巴的数量级,大多数位于20-60巴;总结了地壳中代表性岩石在地壳温度、压力条件下,粘滑及脆性剪切破裂时的应力降,它们与温度、压力、岩性、含水矿物的存在有关.取值范围是从零到几千巴数量级;讨论了地震断层的物理状态,指出地震应力降是一种平均结果,并由于静态理论忽略了断层面破裂所消耗的能量,所以地震应力降比实际的应力降要低.      

2019年9月16日张掖5.0级地震前多尺度电磁异常现象

2019年9月16日甘肃张掖发生5.0级地震，地震发生前既有空间范围跨度较大的地磁低点位移异常，也有单台电磁扰动异常；既有震前2年开始出现的山丹台视电阻率的年变形态畸变，也有震前3个月之内出现的高台钻孔应变和高台大庄低频电磁扰动异常。本次地震震级不高却记录到丰富的电磁场的异常信号，表明该地区处于地震电磁异常的敏感区。高台钻孔应变在震前观测到同步的异常变化，揭示孕震区应力状态发生了显著的变化。     

岷县M_S6.6地震震源机制及构造应力研究

利用甘肃省测震台网观测到的主震波形记录的初动符号求解了2013年7月22 日岷县Ms6.6地震主震的震源机制,并与哈佛及usgs发布的震源机制进行了对比,对这一地区过去发生过的若干次Mb4.5以上的地震也利用初动符号求解了震源机制,发现与Ms6.6地震的震源机制形态较为相似.进而利用2010年至2011年甘东南宽频带流动台阵的大量近震资料,对在震中距50 km范围内,并且接近岷县Ms6.6地震发震断裂临潭-宕昌断裂的中小地震进行了检索,对检索到的地震进行初动识别后得到初动数目大于10个、并且对震源包络良好的中小地震31个,利用小震的震源机制解求解了该区域的区域应力场.结果表明这一区域的主压力方向为NEE方向.     

Variation of seismic source parameters and stress drops within a descending slab and its implications in plate mechanics

A least-squares searching technique has been developed to estimate the source dimensions of intermediate and deep focus earthquakes using azimuthal variations of body wave pulse-widths. With this method and also amplitude data, modes of rupture propagation, seismic moments, and stress drops of 17 intermediate and deep focus earthquakes in the Tonga-Kermadec region have been determined in order to investigate variations in source properties and the state of stress within the descending slab there. Three different modes of rupture; unilateral, bilateral, and circular faults, are compared and tested against observations. Results indicate that the unilateral fault is the best model for most of the earthquakes studied. Stress drops of the 17 events vary within a very large range, from 20 bar to about 4.6 kbar, and change significantly with depth. The magnitude of stress drops for depths between 220 and 430 km is very much higher than at shallower depths. This change in stress drop magnitude at about 220 km-depth seems to reflect a change in material properties both in the mantle and within the slab. Two regions of high stress drop are observed at depths of about 360 and 640 km. A relative minimum of stress drop is found at about 450–560 km where the earthquake frequency is particularly high. Earthquakes at the northern end to the Tonga arc, where the Benioff zone is laterally bent, show systematically higher stress drops than other events at comparable depths, but away from the bend. Also, events in regions of low seismicity appear to have higher stress drops than those in regions of high seismicity. The upper bound of seismic efficiency is found to decrease with depth, implying an increase of frictional force with depth at the earthquake source.