东祁连山北缘断裂带基于深度学习的密集台阵地震事件快速检测与定位研究

为监测东祁连山北缘断裂带附近的地震活动性,布设包含240台短周期地震仪的面状密集台阵,进行约30 d的连续观测。首先使用基于深度学习的多台站地震事件检测算法（CNNDetector）进行地震事件检测,然后使用震相拾取网络（PhaseNet）对地震事件进行P波和S波到时拾取,其次使用震相关联算法（REAL）进行震相关联及初定位,最后使用双差定位（hypoDD）进行地震重定位,最终的精定位地震目录中共有517个地震。在密集台阵观测期间,中国地震台网正式地震目录中共有39个位于台阵内的地震事件,相比而言,密集台阵检测到大量小于0级的地震。因此通过布设密集台阵,可提高活动断裂微地震活动性的监测能力。与历史地震空间分布相比,密集台阵地震精定位分布具有较好的一致性,表现出更明显的线性分布特征。基于地震分布,发现研究区域存在与地表断层迹线走向不同的隐伏活跃断裂。     

姚安地震序列的震源参数研究

利用昆明区域数字遥测台网记录的姚安地震序列资料，结合姚安震区流动数字化台网的近震源观测资料，使用波谱分析法测算婉安地震序列的震源力学参数，给出S波的计算结果，并进行讨论。同时，对区域数字遥测台网和震区流动为流动数字化台网同时记录的39个地震采用同一模式计算出的震源参数进行了对比讨论。     

2011年1月安徽安庆Ms4.8地震震源区三维速度结构与发震构造讨论

The Anqing MS4.8 earthquake occurred on January 19, 2011, with the epicenter lying in the foreland deformation belt along the Yangtze River of the lower Yangtze block. After the earthquake, the field work team surveyed and collected building damage data, calculating and obtaining more accurate intensity distributions. The focal mechanism of the main shock was calculated tentatively using digital seismic wave data from provincial digital seismic networks using the FOCMEC program and the first motions of P, SV and SH waves with their amplitude ratios. Using the location results of the main shock and aftershocks by the Anhui seismic network, combining the three-dimensional crust velocity structure imaging results of the focal region by seismic tomography, and referring on intensity distribution of the elliptic major axis’ predominant direction, we conclude by comprehensive analysis that the NE-trending Susong-Zongyang fault is possibly the causative fault of the Anqing earthquake.     

Seismic Imaging of a Bimaterial Interface Along the Hayward Fault,CA, with Fault Zone Head Waves and Direct P Arrivals

We observe fault zone head waves (FZHW) that are generated by and propagate along a roughly 80 km section of the Hayward fault in the San Francisco Bay area. Moveout values between the arrival times of FZHW and direct P waves are used to obtain average P-wave velocity contrasts across different sections of the fault. The results are based on waveforms generated by more than 5,800 earthquakes and recorded at up to 12 stations of the Berkeley digital seismic network (BDSN) and the Northern California seismic network (NCSN). Robust identification of FZHW requires the combination of multiple techniques due to the diverse instrumentation of the BDSN and NCSN. For single-component short-period instruments, FZHW are identified by examining sets of waveforms from both sides of the fault, and finding on one (the slow) side emergent reversed-polarity arrivals before the direct P waves. For three-component broadband and strong-motion instruments, the FZHW are identified with polarization analysis that detects early arrivals from the fault direction before the regular body waves which have polarizations along the source-receiver backazimuth. The results indicate average velocity contrasts of 3–8 % along the Hayward fault, with the southwest side having faster P wave velocities in agreement with tomographic images. A systematic moveout between the FZHW and direct P waves for about a 80 km long fault section suggests a single continuous interface in the seismogenic zone over that distance. We observe some complexities near the junction with the Calaveras fault in the SE-most portion and near the city of Oakland. Regions giving rise to variable FZHW arrival times can be correlated to first order with the presence of lithological complexity such as slivers of high-velocity metamorphic serpentinized rocks and relatively distributed seismicity. The seismic velocity contrast and geological complexity have important implications for earthquake and rupture dynamics of the Hayward fault, including a statistically preferred propagation direction of earthquake ruptures to the SE.     

1927年古浪8级大震区小震重新定位及问题讨论

联合利用甘肃及周边测震台网记录的古浪及周边地区4 592次地震的P波绝对到时和相对到时资料,采用双差地震定位方法对古浪震源区小震进行重新定位后发现,皇城-双塔断裂带东、西两段表现出不同的力学运动性质,西段以逆冲运动为主,地震主要发生在断裂的下盘;而东段地震却主要发生在上盘,断层活动以局部拉张为主。还首次发现在皇城-双塔断裂带的中段与主破裂呈垂直方向存在一条主震发生时新产生的共轭断层,基于小震的断层面参数反演显示该断裂是一高倾角运动性质以右旋为主兼具正断的断裂。     

山西数字地震台网监测能力分析

根据山西数字测震台网布局和实际获得的参数,运用反推方法,对测震台网的监测能力进行分析,运用记录的地震事件进行检验,表明台网监测能力的理论分析结果与实际观测结果基本相符;山西数字测震台网对山西省地区的监测能力均达到2．0级以上,大部分地区的监测能力达到1．5级以上,少部分地区的监测能力达到1．0级以上。其中,朔州市、吕梁市与运城市的监测能力需进一步加强。     

The East Thuringian Seismic Network

The East Thuringian Seismic Network (OTSN) was installed in 1997. It started its operation with five and now consists of six seismic stations, the GRSN (German Regional Seismic Network) station MOX and a control and analysis centre. All stations are equipped with 3-component GÜRALP and short-period seismometers, RefTek 24-bit data acquisition systems (dynamic range 23.5 bit), hard disks, GPS-receivers, modems and communication computers for dial-up purposes. The seismic signals are sampled at 100 Hz and stored on the hard disk. Simultaneously, the signals are processed by a STA/LTA detector which generates an extended event list. The central station calls these event lists once per day, analyses them, produces a list of real seismic events and calls the waveform data for these events only from the single stations. All stations operate completely autonomously and the whole system works automatically, but all operations can also be carried out interactively. The event analysis is performed manually using common seismic analysis programs. The main purpose of installing the seismic network is to investigate the local seismicity, its relation to recent tectonics, the stress field and structure of the upper crust in order to render more precisely the seismic hazard of East Thuringia. A further aim of the network is to improve the seismic monitoring situation for the neighbouring regions, especially the Vogtland/Northern Bohemia and the Western Saxony area.     

雅江6.0级地震前后的波谱变化

利用成都区域数字化地震台网中的郭达山台、蒙顶山台和鲜家坪台记录的数字波形资料，对2001年2月23日雅江6．0级地震发生前后的39个前、余震作了波谱分析。结果表明这3个台的拐角频率比值在主震前后都出现了不同的变化趋势。并且不同台站之间的变化趋势也存在差异。     

由地震分布丛集性给出断层参数的一种新方法

由于大范围内地质构造的复杂性和介质的非均匀性,发震断层面的几何形态一般十分复杂.如果大地震的破裂过程涉及多个断层的活动,则发震断层并非是单一断层平面,而是多个断层面的组合.利用地震空间位置分布丛集性,即震源点成丛位于断层面附近的假设,结合稳健扩充算法和主成分分析给出一种可以重构活断层网络三维空间结构的新方法.该方法每次从震源点集中处开始,利用假设检验扩充子断层面,并得到多个子断层面.接着按震源点属于最近断层面的准则把各子断层面内的震源点进行竞争,并根据一定假设合并和删除一些子断层面,最后用主成分分析确定每个子断层面参数.于是可根据地震事件目录给出一组矩形区域来描述断层面网络结构,其中每个矩形断层面由其位置、走向和倾角确定.通过计算机模拟发现,新方法可成功地重建模拟地震目录的断层面,最后用于南加州1992年6月28日发生的Landers地震部分余震目录中,得到各个子断层面参数与已知地质破裂或隐伏断层相当一致.     

2019年甘肃张掖M5.0地震余震序列重定位

本文使用祁连山主动源台网和甘肃省数字测震台网记录到的地震资料,应用双差定位方法和遗传算法对2019年甘肃张掖M5.0地震及其余震进行重定位,获得了30个地震事件的重定位结果,双差定位显示主震位置为38.502°N,100.254°E,震源深度14.7 km。重定位结果显示余震分布在昌马—俄博断裂,较为集中,震源深度主要分布在5～15 km范围内,余震序列沿SW—NE向空间分布。     

The seismogenic fault of the 2010 Efpalion moderate-size seismic sequence (western Corinth gulf,Central Greece)

The 2010 Efpalion seismic sequence with two main moderate earthquake events occurred in the northwestern part of the Corinth Gulf (Central Greece)—a region that has been intensely stretched due to an on-going N–S extensional stress regime. Previous studies assign these two events to activations of (a) two faults dipping to the north with low angles; (b) two faults dipping at high angles, the first dipping to the south, and the second to the north; and (c) two faults dipping at high angles, but the first dips to the north, and the second to the south. The recently proposed TR method for focal mechanisms that identifies the seismogenic fault of an earthquake sequence is applied on the available focal mechanisms of the sequence, and its results are interrelated with the geology of the region, and previous contradictory interpretations. The focal mechanisms constructed with MT inversion define a steep north-dipping normal fault, whereas those constructed with first motions of P-waves define the activation of two adjoining faults that dip with high angles to the SSE and south, respectively, and which are characterized by strain (slip) compatibility. The latter option fits well with the geology of the region that is dominated by a SE to S-dipping horse-tail splay fault zone which exists at the eastern tip of the Nafpaktos Mountain Front. The application of the TR method reveals that the usage itself of different methods for the construction of the focal mechanisms complicates the problem of correctly identifying the seismogenic fault.     

Site characterizations for the Tehran network (TDMMO) in Tehran Region Using Micro-Earthquake,Microtremor and Quarry Blast Data

We did a Study of Horizontal-to-Vertical Component Spectral Ratio in the Tehran seismic zone. Micro-earthquakes, microtremors and quarry blasts data were used as an estimation of the site response in the Tehran zone. Site effects were studied based on horizontal to vertical ratios by the Nakamura׳s technique. Also, we used the spectra of signals for three components with the lowest noise levels for spectral slope studies. The analysis used seismic events from a network of 13 seismic stations by the permanent local seismological network of the Tehran Disaster Mitigation and Management Organization (TDMMO) from 2004 to 2007. The number of events used were different for each station. Quarry blast events were with 1.2≤M_L≤2.2 and micro-earthquakes were with 1.1≤M_L≤4.1.By comparing results for earthquake, microtremor and quarry blast, we could see that there is a significant difference between them. The data showed clear observations, especially in high-frequencies. The H/V spectral ratios indicate dominant frequency for rock/soft site with a higher ratio level for quarry blast ratios, which are comparable to the earthquake results due to their difference sources. The results derived by spectral H/V ratios and spectral analysis may be used to distinguish between local earthquakes and quarry blasts.     

Spatiotemporal evolution of the completeness magnitude of the Icelandic earthquake catalogue from 1991 to 2013

In 1991, a digital seismic monitoring network was installed in Iceland with a digital seismic system and automatic operation. After 20 years of operation, we explore for the first time its nationwide performance by analysing the spatiotemporal variations of the completeness magnitude. We use the Bayesian magnitude of completeness (BMC) method that combines local completeness magnitude observations with prior information based on the density of seismic stations. Additionally, we test the impact of earthquake location uncertainties on the BMC results, by filtering the catalogue using a multivariate analysis that identifies outliers in the hypocentre error distribution. We find that the entire North-to-South active rift zone shows a relatively low magnitude of completeness M_c in the range 0.5–1.0, highlighting the ability of the Icelandic network to detect small earthquakes. This work also demonstrates the influence of earthquake location uncertainties on the spatiotemporal magnitude of completeness analysis.     

A low magnitude seismic sequence near Isernia (Molise,Central Italy) in January 1986

Following the increase in seismic activity which occurred near Isernia (Molise, Central Italy) in January 1986, a digital seismic network of four stations with three-component, short-period seismometers, was installed in the area by the Osservatorio Vesuviano. The temporary network had an average station spacing of about 8–10 km and, in combination with permanent local seismic stations, allowed the accurate determination of earthquake locations during an operating period of about one month. Among the 1517 detected earthquakes, 170 events were selected with standard errors on epicentre and depth not greater than respectively 0.5 and 1.5 km. The most frequent focal depths ranged between 4 and 8 km, while the epicentres distribution covered a small area NE of Isernia of about 10 km². A main rupture zone could not be clearly identified from the spatial distribution of the earthquakes, suggesting a rupture mechanism involving heterogeneous materials. The activity was characterized by low energy levels, the largest earthquake, on January 18, 1986, havingM _D =4.0. The time sequence of events and pattern of seismic energy release revealed a strong temporal clustering of events, similar to the behaviour commonly associated with seismic swarms.     

利用背景噪声互相关研究汶川地震震源区地震波速度变化

利用2007年3月至2009年3月四川数字地震台网的宽频带连续波形资料,通过计算地震背景噪声互相关提取台站对间的经验格林函数,在0.1～0.5 Hz频带下测量每天经验格林函数与参考经验格林函数的走时偏移,进而得到各台站对在该时段内的相对地震波速度变化.结果表明,2008年5月12日汶川M_s8.0级地震造成了震源区地震波速度的急剧降低,最大降幅达0.4%;大致以安县为界,余震带西南部地区在汶川主震后波速降即达到最大值,而东北部地区的最大波速降一般出现在主震后的1~4个月,相对地震波速度变化的这种分段特性与地震序列的时空分布特征有较好的对应关系;在震源区外围的四川盆地也观测到了震后波速降低,而川西高原内部则没有出现显著的波速变化.进一步的分析和计算结果表明主震的静态应力变化和强地面运动引起的地表破坏都不能很好地解释震后波速的急剧降低,地震导致的断层区内部结构破坏和周边介质应力状态改变可能是波速变化的主要原因.     

朝阳地震台数字形变观测仪器故障特征分析

随着数字地震监测仪器的普及和应用,人工、模拟地震观测仪器逐渐被数字仪器所取代,记录方式也由整时记录变成分记录和秒记录。数字仪器在多年运行中,曾出现这样或那样的故障,本文重点通过对多年形变数字观测系统内部所出现的故障,进行分析与讨论,以便在观测工作中更好把握仪器的状况和对仪器出现的故障进行准确分析判定,及时对仪器存在的问题和故障进行解决处理,从而最大程度减少观测数据的断记。     

汶川震前几种低频事件波形分析

列举分析了国外文献所记载的几类低频事件.选择汶川MS8.0地震主断层附近四川省部分台网宽频带数据,采用相应频段,进行带通滤波处理,检测到4种类似的低频事件波形．分别为低频震颤与滑移事件（ETS事件）,深低频地震事件(LFE事件),深低频震动事件（DLF事件）,以及超低频震动事件（VLF事件）．定位分析实例证实,汶川震前的ETS和DLF等低频事件发生在主断层附近,表明大震发生之前龙门山断裂带附近有低频事件发生,主要为ETS和VLF两类事件及少量DLF事件．因有远震记录与LFE事件时间相近,无法确认此类事件是否存在．低频事件作为天然地震目录的补充,可为大震前兆和触发机理研究提供新的探索方向．      

基于模板匹配定位法的江苏盐城附近微震检测和构造分析

利用基于GPU加速的匹配定位法和双差定位法,对江苏盐城及邻区18个台站记录的2009~2018年共10年的连续地震资料进行分析。首先从台网目录中挑选211个地震事件作为模板事件,使用匹配定位技术对江苏盐城附近连续10年的地震进行检测和识别,共识别出1349个地震事件,约为台网目录地震事件的3倍,最小完备震级由台网目录的M_L1.9降为M_L1.2。然后利用双差定位法对检测到的地震事件进行精定位,精定位的结果揭示：建湖地区的地震密集带与洪泽-沟墩断裂有关,震源深度优势分布为5~20km,断裂两侧震源深度有显著差异,断裂带倾向NW;射阳震群震源深度比建湖震群有所加深,优势分布为10~25km,震源深度由南东向西北逐渐变浅;宝应地区地震丛集分布;东台地区由于模板事件相对较少,扫描定位后,地震事件在陈家堡-小海断裂带附近零星分布。研究结果为研究盐城地区的地震活动性、发震断层的深部构造提供了基础数据支撑。     

城市活断层探测信息系统的设计与实现——以福州市活断层信息管理系统为例

以福州市活断层信息管理系统为例,提出了城市活断层探测信息系统建设的目标,分析了以GIS技术为支持的、面向对象的设计方法及系统结构与功能。系统在局域网内采用C/S模式,在广域网中采用B/S模式,具有用户界面、应用程序和基础数据的3层结构。探测成果数据库按照分类、分层存贮,按专题组织查询的方式管理。城市活断层探测信息管理系统以活断层探测成果数据库为基础,空间分析为支撑,集地质、地球物理、地球化学、综合查询及专题分析应用为一体,具备活断层探测及分析研究成果分类与综合查询、展示、分析等功能,这一系统的建立可为活断层研究的定量化提供坚实的数据基础与技术平台,为城市规划、土地利用等防震减灾工作的开展提供科学依据     

广东数字地震台网‘十五’系统的几种地震定位方法的定位效果分析

选取广东省‘十五’数字地震台网2007年6-9月试运行以来记录到的32次地震事件,运用地震台网地震速报及地震编目使用的几种常规地震定位软件,并将其结果与‘九五’编目产出的结果进行了比较,结果表明：对于网内地震。单纯型定位法及HYP02000程序的定位法结果稍优于Hyposat定位法：对于网缘地震,3种定位程序得到的结果相差不大。