近场震级起算函数确定与爆炸余震震级计算

在天然地震背景下，由于现有的起算函数在0—5km范围内是一个常数，因此，对于震源深度较浅的小地震震级的测定遇到了困难，本文通过理论计算和爆炸地震波实际测量两种方法，确定了近场0—5k瑚范围内的震级起算函数。用本文确定的震级起算函数计算了两次爆炸余震序列事件的震级，绝大多数的余震震级非常小，主要分布在-0．5—1．0级之间，余震序列的M-t图与一般强余震M-t图明显不同，它不仅存在反映较大震级的正向柱状线，而且还存在反映较小震级的负向短柱状线。     

2013年芦山地震序列震源机制与震源区构造变形特征分析

基于四川区域地震台网记录的波形资料,利用CAP波形反演方法,同时获取了2013年4月20日芦山M7.0级地震序列中88个M≥3.0级地震的震源机制解、震源矩心深度与矩震级,进而利用应变花（strain rosette）和面应变（areal strain）As值,分析了芦山地震序列震源机制和震源区构造运动与变形特征.获得的主要结果有：（1）芦山M7.0级主震破裂面参数为走向219°/倾角43°/滑动角101°,矩震级为M_W6.55,震源矩心深度15 km.芦山地震余震区沿龙门山断裂带走向长约37 km、垂直断裂带走向宽约16 km.主震两侧余震呈不对称分布,主震南西侧余震区长约27 km、北东侧长约10 km.余震分布在7~22 km深度区间,优势分布深度为9~14 km,序列平均深度约13 km,多数余震分布在主震上部.粗略估计的芦山地震震源体体积为37 km×16 km×16 km.（2）面应变As值统计显示,芦山地震序列以逆冲型地震占绝对优势,所占比例超过93%.序列主要受倾向NW、倾角约45°的近NE-SW向逆冲断层控制;部分余震发生在与上述主发震断层近乎垂直的倾向SE的反冲断层上;龙门山断裂带前山断裂可能参与了部分余震活动.P轴近水平且优势方位单一,呈NW-SE向,与龙门山断裂带南段所处区域构造应力场方向一致,反映芦山地震震源区主要受区域构造应力场控制,芦山地震是近NE-SW向断层在近水平的NW-SE向主压应力挤压作用下发生逆冲运动的结果.序列中6次非逆冲型地震均发生在主震震中附近,且主震震中附近P轴仰角变化明显,表明主震对其震中附近局部区域存在明显的应力扰动.（3）序列整体及不同震级段的应变花均呈NW向挤压白瓣形态,显示芦山地震震源区深部构造呈逆冲运动、NW向纯挤压变形.各震级段的应变花方位与形状一致,具有震级自相似性特征,揭示震源区深部构造运动和变形模式与震级无关.（4）不同深度的应变花形态以NW-NWW向挤压白瓣为优势,显示震源区构造无论是总体还是分段均以NW-NWW向挤压变形为特征.但应变花方位与形状随深度仍具有较明显的变化,可能反映了震源区构造变形在深度方向上存在分段差异.（5）芦山地震震源体尺度较小,且主震未发生在龙门山断裂带南段主干断裂上,南段长期积累的应变能未能得到充分释放,南段仍存在发生强震的危险.     

2016年8月21日-10月24日河北开平ML 4.7震群分析

2016年8月21日17时15分,河北省唐山市开平区（39.70°N,118.35°E）发生M_L 3.5地震,震源深度6 km。据河北省快报目录,8月21日至10月24日共发生可定位小震694次,最大地震为9月10日M_L 4.7地震。计算本次震群序列参数,分析其物理特性。精定位结果显示,M_L 4.7震群集中在唐山-古冶断裂,属唐山老震区余震活动。与该区同等震级地震相比,震群中几次3级以上地震视应力水平较低,震源机制一致性较好,表明该区存在较为一致的稳定应力场。震群活动显示,该震群为非典型前兆性震群。分析结果对正确了解此次震群特征及判断序列发展趋势具有较高的帮助作用。     

中国大陆7级大地震强余震震级和空间分布特征

本文研究了中国大陆1966年以来15次7.0～7.9级地震序列强余震空间分布和震级分布特征。 研究结果表明: ① 强余震与主震震级差(ΔM)与频度(N)的统计关系服从指数分布, 统计得到了全部序列平均B值为0.72, 12个走滑型地震序列平均B值为0.73; ② 走滑型地震序列强余震优势分布范围是5~59 km, 非走滑型序列优势分布为10~29 km, 并且强余震与主震震中距离服从正态分布。     

川滇地区烈度计台站测定震级校正分析

烈度计台与测震台的布设环境、仪器类型不同,所测定的震级值存在一定差异。收集2017-2019年川滇地区301个烈度计台站记录的46次M_L 3.0以上地震,进行震级校正。统计烈度计实测震级值与测震台网平均震级值的偏差,对原量规函数进行修正,进而做台站校正。综合修正后,利用量规函数和台站校正值重新计算烈度计震级,结果表明：在震中100 km范围内,烈度计测定震级偏差平均值由校正前的0.145降低至0.033,标准差由0.382降低至0.295,离散度减小;校正后的烈度计震级结果较优,说明本研究获得的量规函数和台站校正值更加适用于川滇地区烈度计台站的震级计算。     

Use of Potential Foreshocks to Estimate the Short-term Probability of Large Earthquakes, Tohoku, Japan

This study seeks to construct a hazard function for earthquake probabilities based on potential foreshocks. Earthquakes of magnitude 6.5 and larger that occurred between 1976 and 2000 in an offshore area of the Tohoku region of northeast Japan were selected as events for estimating probabilities. Later occurrences of multiple events and aftershocks were omitted from targets. As a result, a total of 14 earthquakes were employed in the assessment of models. The study volume spans 300 km (East-West) × 660 km (North-South) × 60 km in depth. The probability of a target earthquake occurring at a certain point in time-space depends on the number of small earthquakes that occurred per unit volume in that vicinity. In this study, we assume that the hazard function increases geometrically with the number of potential foreshocks within a constrained space-time window. The parameters for defining potential foreshocks are magnitude, spatial extent and lead time to the point of assessment. The time parameter is studied in ranges of 1 to 5 days (1-day steps), and spatial parameters in 20 to 100 km (20-km steps). The model parameters of the hazard function are determined by the maximum likelihood method. The most effective hazard function examined was the following case: When an earthquake of magnitude 4.5 to 6.5 occurs, the hazard for a large event is increased significantly for one day within a 20 km radius surrounding the earthquake. If two or more such earthquakes are observed, the model expects a 20,000 times greater probability of an earthquake of magnitude 6.5 or greater than in the absence of such events.     

内蒙古地区地方性震级的量规函数研究

选取2008年1月~2015年11月内蒙古测震台网81个台站所记录的6342次地震事件,基于震级残差统计方法,计算了81个台站单台震级与台网平均震级的偏差、平均偏差和标准偏差。分析认为,BHS等6个台站震级偏差较大的原因可能是台站场地响应放大、台基风化等。台基校正前、后单台震级平均偏差值ΔMLi随震中距的变化曲线显示,曲线形态基本未有大的改变,台基校正后较之前震级平均偏差绝对值降低0.01,表明台基对地方性震级偏差的影响不大。同时,进行了81个台站的台基校正获得了内蒙古新量规函数,结果表明,全国量规函数除了震中距为0~120km时适合于内蒙古地区以外,其余情况下均偏高,不符合内蒙古地区的特征。因此,本文修定了全国量规函数,得到了校正后的内蒙古地区量规函数。     

广西测震台网台站地方性震级偏差分析

选用广西数字化测震台网2008—2020年记录的广西及邻区1 251个M_L ≥ 2.0地震事件震相资料,采用震级残差统计方法,获取广西51个地震台单台震级与台网平均震级的平均偏差和标准差,分析观测仪器类型、台基场地响应和震中距等因素对震级偏差的影响,进而提出台基校正值,修正区域量规函数。结果发现,南宁、天等、北海等15个地震台站的震级偏大,桂林、贺州、天峨等16个地震台站的震级偏小,崇左、灵山、平果等20个地震台站震级适中;在单台震级共14 784个样本中,震级偏差集中在-0.4—0.4,呈正态分布;震级偏差受台基场地响应和震中距因素影响明显,当场地响应值大于1.0时震级偏大,小于1.0时震级偏小,等于1.0时震级较为适合,当震中距在70 km范围内时单台震级偏小,当震中距在70—300 km时单台震级较为适合,当震中距在300—550 km时,单台震级稍有偏大。修正后的区域量规函数和台基校正值,可有效提高广西测震台网测定震级的准确性。     

江西数字地震台网近震震级偏差与量规函数关系的研究

采用江西数字地震台网数字地震记录资料,选取自2007年10月正式运行至2009年12月所记录的138次ML≥1.5的地震事件,计算了各台站单台震级与台网平均震级的偏差、平均偏差和标准偏差,从震级偏差频次分布、量规函数、平均周期等因素对单台震级的影响上作了定量统计和分析。结果表明:①除九江、赣州、石城、都昌、高安5个台的震级与台网的平均震级偏差比较大外,其余台站均比较小;②目前所用量规函数在震中距小于40 km时偏小,大于330 km时偏大,给出了量规函数校正值,③平均周期小于0.17 s时,变得极不稳定,离散程度明显增大,这种情况应该是由于单台震中距超过300 km的样本数太少所导致的。     

2015年5月云南双柏ML4.1地震活动机理初探

2015年5月19日9时58分,云南双柏、峨山一带出现密集的小震活动,并于6月14日发生M_L4.1地震,形成显著的震群事件。本文利用双差定位法对该震群进行精定位,结果显示,重新定位后震中分布优势方向更明显,主要沿绿汁江南段断裂呈NNE向分布,震源深度为6～12km,其中,又以8～10km最具优势。与原始数据相比,重定位后残差明显减小,走时残差平方和由原来的0.303s降为0.034s,震源位置估算误差在EW方向平均为0.21km,在NS方向平均为0.173km,在垂直方向平均为0.175km;利用广义极性振幅技术（GPAT）方法,计算得到了24个M_L≥2.5地震的震源机制解,结果显示,此次震群的震源机制类型绝大部分表现为正断性质,与该区历史地震多为走滑的结果有所差异。结合震区附近的龙门水库蓄水水位和该震群的频度-震级关系分析认为,双柏震群活动与水库蓄水过程密切相关,该震群的发生是龙门水库水体载荷加载而引起正断层产生错动的结果。     

1974年和1979年江苏省溧阳两次中等强度地震的前兆性空区.

1974年4月22日、1979年7月9日在江苏省溧阳地区先后发生5.8级、6.3级(ML)两次地震.在这两次地震前约23个月,其周围200多公里范围内出现地震空区图象.1974年5.8级地震前16个月,在240公里范围内没有发生小地震;临近震前7个月空区活化,爆发一系列小地震.1979年6.3级地震前15个月,在100公里范围内和240公里范围外发生一些小地震,形成环形空区;临近地震前7个月,约200公里范围内均无小震活动.根据两次主震等震线,主、余震展布和震源机制结果认为,它们是在北东东向压应力和北北西向张应力作用下,发生在同一震源区的不同期共轭地震.两次地震空区图象的形成、发展和消失过程,描绘了区域应力持续作用下,中等均匀程度的地壳不均匀应变的演化过程.      

2013年甘肃岷县—漳县M 6.6地震序列精定位研究

采用双差定位法对2013年7月22日甘肃岷县—漳县交界地区M 6.6地震及主震后48小时内388次余震序列进行重新定位,得到350个精定位地震数据。结果表明,余震优势展布以北东向较大倾角的铲状结构为特征,长约12 km,以主震为中心两侧对称分布;震源深度主要集中在4—10 km范围内,但余震震级由10 km左右深度的3—4级向3 km深度之上近地表的2—3级迁移变化;余震分布清晰呈现双层结构,较深层分布在4—10 km深度,而较浅层分布3 km深度之上,2层之间地震分布较少。分析认为,浅层地震可能为本次地震地表破坏较强原因之一。震源深度剖面显示,破裂面向NE倾斜,推测此次地震的发震断裂为临潭—宕昌断裂。     

新疆南天山环境应力场特征

基于新疆强震固定台和流动观测记录的主要和余震加速度资料，选用了三个分向记录都完整的３７次地震。震级范围为１．８－６．８级，震中距为几至几十公里。根据用位错理论二维断裂力学模式推导的震源峰值、加速度与环境剪应力场关系式计算了新疆南天山环境剪应力值。计算结果表明，新疆南天山环境应力平均值偏高，这与新疆处于特殊构造环境条件有关。     

Rapid estimation of the hazard posed by strong aftershocks for Kamchatka and the Kuril Islands

This paper deals with the rapid estimation of the hazard posed by strong aftershocks for Kamchatka and the Kuril Islands based on the 12-hour aftershocks, namely, their rate, time of expectation, and maximum magnitude. The data set consists of main shocks and aftershocks as reported in the Catalog of the Kamchatka Branch of the Geophysical Survey, Russian Academy of Sciences (GS RAS) for 1968–2016. We used both the Gutenberg–Richter relation and the Omori–Utsu law to find that the aftershock rates in two time intervals are connected by a relationship of proportionality, with the constant of proportionality being independent of the lowest magnitude of these earthquakes. With this property in mind, we calculated the constants of proportionality for estimating the rate of aftershocks with a magnitude above threshold values based on the data for the first 12 hours after the main shock. We have derived easily remembered rules for estimating the aftershock rates that can be expected for 5 days and for 1 month with magnitudes above a fixed value based on the 12-hour aftershock observations. We also derived empirical regression relations to estimate the magnitude of the largest aftershock that can be expected to occur during 1 year after the main shock and the time of the last aftershock to occur whose magnitude is 5.2 or greater.     

Spatio-temporal characteristics of aftershocks and seismogenic structure of the 2011 MW9.0 Tohoku earthquake,Japan

The Tohoku megathrust earthquake, which occurred on March 11, 2011 and had an epicenter that was 70 km east of Tohoku, Japan, resulted in an estimated ten's of billions of dollars in damage and a death toll of more than 15 thousand lives, yet few studies have documented key spatio-temporal seismogenic characteristics. Specifically, the temporal decay of aftershock activity, the number of strong aftershocks (with magnitudes greater than or equal to 7.0), the magnitude of the greatest aftershock, and area of possible aftershocks. Forecasted results from this study are based on Gutenberg-Richter's relation, Bath's law, Omori's law, and Well's relation of rupture scale utilizing the magnitude and statistical parameters of earthquakes in USA and China (Landers, Northridge, Hector Mine, San Simeon and Wenchuan earthquakes). The number of strong aftershocks, the parameters of Gutenberg-Richter's relation, and the modified form of Omori's law are confirmed based on the aftershock sequence data from the M_W9.0 Tohoku earthquake. Moreover, for a large earthquake, the seismogenic structure could be a fault, a fault system, or an intersection of several faults. The seismogenic structure of the earthquake suggests that the event occurred on a thrust fault near the Japan trench within the overriding plate that subsequently triggered three or more active faults producing large aftershocks.     

天山北部强震活动对区域应力扰动的分析以2012年伊犁M6.6地震和2017年精河M6.6地震为例

天山地区为典型地震活跃区, 为定量分析该构造活跃区强震对周边构造变形和地震活动的影响, 本文基于地震位错理论和岩石圈分层模型计算了天山北部近期发生的2012年伊犁和2017年精河两次M6.6地震对周围地壳形变和应力的影响。 计算结果显示伊犁地震和精河M6.6地震引起震中附近地表同震位移达数厘米, 地表同震应变量级约为10^-7; 对比天山北部地区年平均构造形变特征, M6.6强震释放了震中附近近十年的构造主压应变积累; 地震引起震中附近(80 km内)同震库仑应力变化大于1 kPa, 而距震中较远区域活动断层上库仑应力变化微弱。 结合天山北部现今地壳变形特征及区域地震分布, 初步推测两次M6.6地震的发生对震后余震有显著的触发作用, 而对区域后续微震活动的影响微弱。     

Ometepec-Pinotepa Nacional,Mexico Earthquake of 20 March 2012 (Mw 7.5): A preliminary report

An analysis of local and regional data produced by the shallow, thrust Ometepec-Pinotepa Nacional earthquake (M_w 7.5) of 20 March 2012 shows that it nucleated at 16.254°N 98.531°W, about 5 km offshore at a depth of about 20 km. During the first 4 seconds the slip was relatively small. It was followed by rupture of two patches with large slip, one updip of the hypocenter to the SE and the other downdip to the north. Total rupture area, estimated from inversion of near-source strong-motion recordings, is ~25 km × 60 km. The earthquake was followed by an exceptionally large number of aftershocks. The aftershock area overlaps with that of the 1982 doublet (M_w 7.0, 6.9). However, the seismic moment of the 2012 earthquake is ~3 times the sum of the moments of the doublet, indicating that the gross rupture characteristics of the two earthquake episodes differ. The small-slip area near the hypocenter and large-slip areas of the two patches are characterized by relatively small aftershock activity. A striking, intense, linear NE alignment of the aftershocks is clearly seen. The radiated energy to seismic moment ratios, (E_s/M₀), of five earthquakes in the region reveal that they are an order of magnitude smaller for near-trench earthquakes than those that occur further downdip (e.g., 2012 and the 1995 Copala earthquakes). The near-trench earthquakes are known to produce low A_max. The available information suggests that the plate interface in the region can be divided in three domains. (1) From the trench to a distance of about 35 km downdip. In this domain M~6 to 7 earthquakes with low values of (E_s/M₀) occur. These events generate large number of aftershocks. It is not known whether the remaining area on this part of the interface slips aseismically (stable sliding) or is partially locked. (2) From 35 to 100 km from the trench. This domain is seismically coupled where stick-slip sliding occurs, generating large earthquakes. Part of the area is probably conditionally stable. (3) From 100 to 200 km from the trench. In this domain slow slip events (SSE) and nonvolcanic tremors (NVT) have been reported.The earthquake caused severe damage in and near the towns of Ometepec and Pinotepa Nacional. The PGA exceeded 1 g at a soft site in the epicentral region. Observed PGAs on hard sites as a function of distance are in reasonable agreement with the expected ones from ground motion prediction equations derived using data from Mexican interplate earthquakes. The earthquake was strongly felt in Mexico City. PGA at CU, a hard site in the city, was 12 gal. Strong-motion recordings in the city since 1985 demonstrate that PGAs during the 2012 earthquake were not exceptional, and that similar motion occurs about once in three years.     

河北测震台网单台震级偏差分析

以河北测震台网记录的河北及周边地区地震事件为数据源,计算单台测定震级与台网平均震级的平均偏差、标准偏差,采用统计、对比、归纳分析等方法,分析偏差的分布情况,依据震中距分段计算平均偏差,得到震级偏差的分布规律及相应校正值;最后通过对量规函数、台基岩性等进行校正,对比拟合出符合河北台站特点的新量规函数,使误差精度在规定范围之内。     

丁青地区地震重定位、震源机制及其发震构造初步分析

文中利用青海省地震台网的宽频带数字记录,通过CAP反演等方法获取了西藏丁青8次MS≥3.0地震的震源机制解(1次地震的震源机制解来自USGS).结果显示,7次地震以正断破裂为主,兼具少量右旋走滑分量,断层优势走向为NNE,P轴的优势方位为SWW,T轴的优势方位为SEE.同时,利用双差相对定位法获得了217个地震的重定位...     

2005年新疆克孜尔震群的重新定位

用双差地震定位法对2005年9月23日克孜尔震群进行重新定位。 从平面上, 重新定位地震集中分布在一个长约14.5 km, 宽约 9.0 km的长方形内, 其长轴为N30°W向, 与克孜尔断裂近乎垂直。 从震源深度来看, 重新定位地震的震源深度全部分布在21 km以内, 集中分布在10~19 km, 平均深度为13.6 km; 震群中绝大部分小震发生在沉积层内, 而震级较大地震基本发生在结晶地壳的上地壳内。 其剖面图显示, 这次震群是从结晶地壳开始沿着N30°W方向向上破裂至沉积层。 根据震区附近断裂性质和该区历史小震震中分布分析认为, 克孜尔水库库区附近可能存在两条共轭断裂, 右翼断裂可能是这次震群的发震构造。