Regional minimum 1-D P-wave velocity model for a new seismicity catalogue with precise and consistent earthquake locations in southern Iran

For faster and more robust ray tracing in 1-D velocity models and also due to the lack of reliable 3-D models, most seismological centers use 1-D models for routine earthquake locations. In this study, as solution to the coupled hypocenter-velocity problem, we compute a regional P-wave velocity model for southern Iran that can be used for routine earthquake location and also a reference initial model for 3-D seismic tomography. The inversion process was based on travel time data from local earthquakes paired reports obtained by merging the catalogues of Iranian Seismic Center (IRSC, 6422 events) and by the Broadband Iranian National Seismic Network (BIN, 4333 events) for southern Iran in the period 2006 through July 2017. After cleaning the data set from large individual reading errors and by identifying event reports from both networks belonging to same earthquake (a process called event pairing), we obtained a data set of 1115 well-locatable events with a total number of 24,606 P-wave observations. This data set was used to calculate a regional minimum 1-D model for southern Iran as result of an extensive model search by trial-and-error process including several dozens of inversions. Significantly different from previous models, we find a smoothly increasing P-velocity by depth with velocities of 5.8 km/s at shallow and velocities of 6.4 km/s at deepest crustal levels. For well-locatable events, location uncertainties are estimated in the order of ±?3 km for epicenter and double this uncertainty for hypocentral depth. The use of the minimum 1-D model with appropriate station delays in routine hypocenter location processing will yield a high-quality seismic catalogue with consistent uncertainty estimates across the region and it will also allow detection of outlier observations. Based on the two catalogues by IRSC and BIN and using the minimum 1-D model and station delays for all stations in the region, we established a new combined earthquake catalogue for southern Iran. While the general distribution of the seismicity corresponds well with that of the two individual catalogues by IRSC and BIN, the new catalogue significantly enhances the correlation of seismicity with the regional fault systems within and between the major crustal blocks that as an assembly build this continental region. Furthermore, the unified seismic catalogue and the minimum 1-D model resulting from this study provide important ingredients for seismic hazard studies.     

20世纪云南地区地震记录完全性评价

通过对1901～2000年云南地区5级以上地震记录完全性分析,发现20世纪早期云南地震漏载仍然严重,30年代以后5级以上地震记录较为完全,其中滇西南为地震记录的主要漏载地区。根据b值估算得到20世纪云南地区漏载5级地震143次、6级地震6.6次,这是地震活动性研究需要考虑的重要因素。60年代后地震活动的起伏与地震监控能力无关。     

An improved earthquake catalogue (<Emphasis Type="Italic">M</Emphasis> ≥ 4.0) for Turkey and its near vicinity (1900–2012)

Many catalogues, agency reports and research articles have been published on seismicity of Turkey and its surrounding since 1950s. Given existing magnitude heterogeneity, erroneous information on epicentral location, event date and time, this past published data however is far from fulfilling the required standards. Paucity of a standardized format in the available catalogues have reinforced the need for a refined and updated catalogue for earthquake related hazard and risk studies. During this study, ~37,000 earthquakes and related parametric data were evaluated by utilizing more than 41 published studies and, an integrated database was prepared in order to analyse all parameters acquired from the catalogues and references for each event. Within the scope of this study, the epicentral locations of M ≥ 5.0 events were firstly reappraised based on the updated Active Fault Map of Turkey. An improved catalogue of 12.674 events for the period 1900–2012 was as a result recompiled for the region between 32–45N° and 23–48E° by analyzing in detail accuracy of all seismological parameters available for each event. The events consist of M ≥ 4.0 are reported in several magnitude scales (e.g. moment magnitude, M_w; surface wave magnitude, M_S; body-wave magnitude m_b; local magnitude M_L and duration magnitude M_d) whereas the maximum focal depth reaches up to 225-km. In order to provide homogenous data, the improved catalogue is unified in terms of M_w. Fore-and aftershocks were also removed from the catalogue and completeness analyses were performed both separately for various tectonic sources and as a whole for the study region of interest. Thus, the prepared homogenous and declustered catalogue consisting of 6573 events provides the basis for a reliable input to the seismic hazard assessment studies for Turkey and its surrounding areas.     

Rating of seismicity and reconstruction of the fault geometries in northern Tien Shan within the project “Seismic Hazard Assessment for Almaty”

The project “Seismic Hazard Assessment for Almaty” has a main objective to improve existing seismic hazard maps for the region of northern Tien Shan and especially for the surroundings of Almaty and to generate a new geodynamic model of the region.In the first step a composite seismic catalogue for the northern Tien Shan region was created, which contains about 20,000 events and is representative for strong earthquakes for the period back to the year 500. For the period of instrumental observation 1911–2006 the catalogue contains data for earthquakes with a body wave magnitude larger than 4. For smaller events with magnitudes up to 2.2 the data are only available since 1980. The composite catalogue was created on the basis of several catalogues from the United States Geologic Survey (USGS), local catalogues from the Kazakh National Data Centre (KNDC) and the USSR earthquake catalogue. Due to the different magnitudes used in several catalogues a magnitude conversion was necessary.Event density maps were created to rate the seismicity in the region and to identify seismic sources. Subsurface fault geometries were constructed using tectonic model which uses fault parallel material flow and is constrained by GPS data. The fault geometry should improve the estimation of the expected seismic sources from seismic density maps.First analysis of the earthquake catalogue and the density maps has shown that nearly all large events are related to fault systems. Annual seismicity distribution maps suggest different processes as the cause for the seismic events. Apart from tectonics, also fluids play a major part in triggering of the earthquakes.Beneath the Issyk-Kul basin the absence of strong seismic activity suggests aseismic sliding at the flat ramp in a ductile crust part and low deformation within the stable Issyk-Kul micro-continent which underthrust the northern ranges of Tien Shan. First results suggest a new partition of the region in tectonic units, whose bounding faults are responsible for most of the seismic activity.     

Completeness Analysis of the Historical Earthquake Catalogue in China

The historical earthquake catalogue of China has lasted more than 3000 years,and most of its data are inferred from historical records.The earthquake catalogue in earlier times is not complete owing to various reasons,so some events are lost.This paper estimates the loss rate of earthquakes with various magnitudes in the historical earthquake catalogue for different time intervals quantitatively by using the Gutenberg-Richter formula and modern instrumental records,which will provide the references for statistic research in seismicity.     

Identifying Seismicity Levels via Poisson Hidden Markov Models

Poisson Hidden Markov models (PHMMs) are introduced to model temporal seismicity changes. In a PHMM the unobserved sequence of states is a finite-state Markov chain and the distribution of the observation at any time is Poisson with rate depending only on the current state of the chain. Thus, PHMMs allow a region to have varying seismicity rate. We applied the PHMM to model earthquake frequencies in the seismogenic area of Killini, Ionian Sea, Greece, between period 1990 and 2006. Simulations of data from the assumed model showed that it describes quite well the true data. The earthquake catalogue is dominated by main shocks occurring in 1993, 1997 and 2002. The time plot of PHMM seismicity states not only reproduces the three seismicity clusters but also quantifies the seismicity level and underlies the degree of strength of the serial dependence of the events at any point of time. Foreshock activity becomes quite evident before the three sequences with the gradual transition to states of cascade seismicity. Traditional analysis, based on the determination of highly significant changes of seismicity rates, failed to recognize foreshocks before the 1997 main shock due to the low number of events preceding that main shock. Then, PHMM has better performance than traditional analysis since the transition from one state to another does not only depend on the total number of events involved but also on the current state of the system. Therefore, PHMM recognizes significant changes of seismicity soon after they start, which is of particular importance for real-time recognition of foreshock activities and other seismicity changes.     

Using Automated, High-precision Repicking to Improve Delineation of Microseismic Structures at the Soultz Geothermal Reservoir

—?An automatic, adaptive, correlation-based algorithm for adjusting phase picks in large digital seismic data sets provides significant improvement in resolution of microseismic structures using only a small fraction of the time and manpower which would be required to re-analyze waveforms manually or semi-automatically. We apply this technique to induced seismicity at the Soultz-sous-Forêts geothermal site, France. The method is first applied to a small, previously manually repicked subset of the catalogue so that we may compare our results to those obtained from painstaking, visual, cross-correlation-based techniques. Relative centroid-adjusted hypocenters show a decrease in median mislocation from 31 to 7?m for preliminary and automatically adjusted picks, respectively, compared to the manual results. Narrow, intersecting joint features not observed in the preliminary hypocenter cloud, but revealed through manual repicking, are also recovered using the automatic method. We then address a larger catalogue of ～7000 microearthquakes. After relocating the events using automatic repicks, the percentage of events clustering within 5?m of their nearest neighbor increases form 5 to 26% of the catalogue. Hypocenter relocations delineate narrow, linear features previously obscured within the seismic cloud, interpreted as faults or fractures which may correspond to fluid propagation paths, or to changes in stress as a result of elevated pore pressures. RMS travel-time residuals for the larger data set are reduced by only 0.2%; however, phase-pick biases in the preliminary catalogue have influenced both the velocity model and station correction calculations, which will affect location residuals. These pick biases are apparent on the adjusted, stacked waveforms and correcting them will be important prior to future velocity model refinements.     

山东乳山震群遗漏地震检测及震源区活动特征分析

对震群活动特征的深入研究可以为区域地震危险性分析和地震活动趋势判断提供有效的依据,但受台网布局和震群位置的影响,地震目录中往往会遗漏一些地震,而地震目录的完整性将会影响震群活动特征分析的可靠性.因此,本文利用基于GPU加速的模板匹配方法对山东乳山震群2014年5月至2015年6月期间固定台站和流动台阵记录的连续波形进行...     

利用历史有感地震目录（M≥3（1／2））研究华北地区地震活动性特征

对新编的华北地区历史有感地震目录（３（１／２）≤Ｍ＜４（１／２））的精度和可信度进行了讨论。认为该地震目录从１４８４年后的记载率较高，它的发震时间、震中位置和震级的精度基本可以满足研究历史地震活动性的需要。它与中国地震目录（Ｍ≥４（３／４））比较，补充了相当数量的３（１／２）≤Ｍ≤４（１／２）的地震。利用历史有感地震目录分析了华北北部部分６级以上的历史地震，结果表明，这些地震在强震发生前具有明显的空区、条带、地震活动性增强、平静等前兆特征，同时，也显示了某些强＊发生前的前震活动和主震之后起伏的强余震活动     

Updated earthquake catalogue for seismic hazard analysis in Pakistan

A reliable and homogenized earthquake catalogue is essential for seismic hazard assessment in any area. This article describes the compilation and processing of an updated earthquake catalogue for Pakistan. The earthquake catalogue compiled in this study for the region (quadrangle bounded by the geographical limits 40–83° N and 20–40° E) includes 36,563 earthquake events, which are reported as 4.0–8.3 moment magnitude (M_W) and span from 25 AD to 2016. Relationships are developed between the moment magnitude and body, and surface wave magnitude scales to unify the catalogue in terms of magnitude M_W. The catalogue includes earthquakes from Pakistan and neighbouring countries to minimize the effects of geopolitical boundaries in seismic hazard assessment studies. Earthquakes reported by local and international agencies as well as individual catalogues are included. The proposed catalogue is further used to obtain magnitude of completeness after removal of dependent events by using four different algorithms. Finally, seismicity parameters of the seismic sources are reported, and recommendations are made for seismic hazard assessment studies in Pakistan.     

The Spanish National Earthquake Catalogue: Evolution,precision and completeness

This paper details the evolution, precision and completeness of the earthquake catalogue compiled by the Spanish National Geographic Institute. Over 100,000 earthquakes are included in this database, occurred in a region embracing Spain, Portugal, Morocco, Andorra and parts of France and Algeria. The catalogue has improved along time, thanks to the development of the seismic network and the upgrades of the routine data acquisition and analysis. The location precision is found to be much better on the Iberian Peninsula than offshore and benefitted especially from the implementation of modern automatic procedures for hypocentral determinations. The different magnitude scales reported in the catalogue, and effects of their changes, are reviewed. In the Iberian Peninsula, Canary Islands and surroundings, detailed successive maps of magnitude of completeness show an overall improvement over the last decades, particularly sudden when the digital broadband network was deployed. Earthquakes are found to be more frequently recorded during nights and weekends, thanks to the lower artificial noise. Despite most blasts have been filtered out of the catalogue, examples of remaining ones are identified by their spatial clustering around mines and quarries, and their timing at the intervals at which blasts are set off (even at night, in contrast to the common assumption that they only occur during daytime). This work highlights the importance of unveiling the spatial and temporal heterogeneities of earthquake catalogues and aims to help future analyses of the seismicity in the region.     

Ergodicity examined by the Thirumalai-Mountain metric for Taiwanese seismicity

Ergodicity is a behavior generally limited to equilibrium states and is here defined as the equivalence of ensemble and temporal averages. In recent years, effective ergodicity is identified in simulated earthquakes generated by numerical fault models and in real seismicity of natural fault networks by using the Thirumalai-Mountain metric. Although the effective ergodicity is already reported for Taiwanese seismicity, an immediate doubt is the unrealistic gridded sizes for discretizing the seismic data. In this study, we re-examined the effective ergodicity in Taiwanese seismicity by using reasonable gridded sizes which corresponded with the location errors in the real earthquake catalogue. Initial time and magnitude cut-off were examined for the validity of ergodic behavior. We found that several subsets extracted from Taiwanese seismicity possessed effectively ergodic intervals and all terminations of these ergodic intervals temporally coincided with the occurrences of large earthquakes (M _L < 6.5). We thus confirm the ergodicity in the crustal seismicity by using the Thirumalai-Mountain metric.     

Geometrical constraints for the configuration of the Vrancea (Romania) intermediate-depth seismicity nest

For a seismogenic area like Vrancea (Romania) with well-defined geometrical features of the seismicity production in space and time, the numerical simulation of the earthquake generation process (e.g. cellular automaton) looks highly attractive. The delimitation, as accurately as possible, of the geometrical features of the seismically active system in the Vrancea subcrustal zone is essential to constrain the simulation modeling. As a first approximation, the seismicity pattern is close to a fault plane NE–SW oriented, extended roughly vertically between 60 and 170 km depth. A characteristic median plane is defined by minimizing the distance of hypocenters. The average distance of the hypocenters to the median plane is around 5 km. However, a more detailed investigation of the geometrical configuration of seismicity indicates a fragmentation of the active body located in the upper mantle in two segments. The seismicity pattern is well approximated by a planar distribution in each segment. In the transition zone, between the upper and lower segment, the hypocenter distribution is more dispersed and shows a disruption among the two planar segments, measured by about 9 km apart laterally one relative to the other. The two segments hosted the major Vrancea events recorded in the last two centuries (for which we have available location of acceptable accuracy). The narrow transition zone at about 100 km depth is interpreted as a weaker segment, possibly caused by a dehydration process or by an infiltration of asthenosphere material from the back side of the South-Eastern Carpathian arc system. It is still debatable if fragmentation in two seismically active segments reflects the existence of two neighbouring separate blocks (upper, continental and lower, oceanic block) or a consequence of a breaking process separating a continental block into two parts. The segmentation of the descending lithosphere and the edge effects are apparently stationary, at least for the time interval since 1985 to the present, for which the earthquake catalogue is reliable (homogeneous).     

2013年甘肃岷县-漳县MS6.6地震余震 序列目录完备性研究 基于对单台记录地震事件震中与震级的估计

中强地震余震序列地震目录编目是否完备、 震源参数是否准确,直接影响余震序列特征分析、 震后趋势快速判断和强余震预测等研究结果的科学性和可靠性. 2013年7月22日甘肃岷县-漳县M_S6.6地震余震序列目录中存在较多单台记录地震事件,地震观测报告仅给出其震级,而未给出震中位置. 由于余震波形间的相互交叠干扰,使得余震最大振幅的测量误差较大,造成地震观测报告给出的单台事件震级误差较大. 精确估计单台记录地震事件的震中和震级,能够补充完善现有地震目录,提高地震目录的完备性. 本文对单台记录地震事件震中和震级的估计不仅限于单个台站,而是通过分析区域台网中多个台站的波形记录实现. 首先以余震序列中震级较大、 波形记录信噪比较高的地震波形作为模板,使用波形互相关震相检测技术,检测单台记录的地震事件在多个台站的震相到时. 如果能在4个以上台站检测到震相,则利用测震台网常用的HYPOSAT方法估计其震中位置,并利用多个台站记录波形与模板地震的振幅比估计其震级. 之后计算主震发生后不同时间的最小完备性震级,并通过线性拟合得到最小完备性震级随时间变化的表达式,以分析此地震余震序列的目录完备性. 经过计算共得到253个单台记录地震事件的震级和其中177个事件的震中位置,其震中空间分布范围与余震序列中其它地震分布范围基本一致. 震级复测以及与人工拾取震相到时误差对比表明,该方法所得震相检测和震级估计结果具有较好的可靠性. 主震及最大余震发生后的短时间内,有较多数量单台事件的目录所给出的震级偏低,分析认为可能受主震与较大余震后续震相以及余震间相互干扰所致. 主震发生0.02—0.3天内,其余震序列最小完备性震级随时间的对数呈线性下降,在0.3天后最小完备性震级稳定在M_L1.1左右.      

Epidemic type aftershock sequence (ETAS) modeling of northeastern Himalayan seismicity

We analyzed the seismicity of northeastern Himalayan region of latitude (25 to 32°?N) and longitude (86–97°?E). The US Geological Survey catalogue is used in this study for a period from 1973 to June 2011. The seismicity of the region is modeled using epidemic type aftershock sequence (ETAS) model. The region is divided in three parts: (1) whole region, (2) subregion I, and (3) subregion II. The magnitude of completeness is found to be 4.6 for all the three regions. The ETAS parameters for all the regions are found same within the standard errors. There is no significant change observed in the seismicity since 1973 based on the ETAS modeling.     

考虑到时误差的地震定位算法及其在四川地区2001-2008年地震定位的应用

精确的地震位置对于地震活动性、地震层析成像和地壳应力场反演具有相当重要的意义,对于地震速报也具有重要的应用价值。将观测到时的不确定性、台站高程、地震震源深度进行约束的同时,根据反演理论给出了地震震源位置精确估计和误差估计的方法。该算法联合考虑Pg波、Sg波、Pn波和Sn波的到时进行反演,数据量的增加可以增强地震位置的准确性,并可同时应用于地方震和区域地震。采用模拟数据对该地震定位算法进行检验发现,该算法在观测数据的不确定性不等时明显优于其他方法。将该算法应用于四川地区2001-2008年间的地震定位,得到的地震位置更加符合地震的丛集性并集中于断裂带附近。这些结果为四川地区的地震活动性、断层构造以及地震层析成像研究打下了基础,并且为汶川地震之前的地震活动前兆研究也提供了有益帮助。     

重庆地区小地震目录完整性分析

根据重庆台网建设的时间阶段性,在对不同震级下限地震频度时间特征分析的基础上,研究了重庆地区不同时段的G-R关系和震级分布特征,并运用z检验方法对不同时段地震目录差异的显著性进行了分析,进而评估了重庆地区1970年以来不同时段的地震目录完整性,为区域地震活动性研究中地震目录的合理运用提供参考依据。     

Re-appraisal of seismicity and seismotectonics in the north-eastern Algeria Part I: Review of historical seismicity

As large destructive seismic events are not frequent in Algeria, anexhaustive knowledge of the historical seismicity is required to have arealistic view of seismic hazard in this part of the world. This research workpresents a critical reappraisal of seismicity in the north-eastern Algeria forseismotectonic and seismic hazard purposes. This part of work focuses onthe seismicity of pre-1900 period for the area under consideration[33^°N-38^°N, 4^°E-9.5^°E]. By going back tothe available documentary sources and evaluating and analysing the eventsin geographical, cultural and historical context, it has been possible toidentify 111 events, from 1850–1899, which are not reported in therecent Algerian catalogue. Several spurious events, reported in standardlistings, have been deleted and nine unknown events have been discovered.It is quite clear that macroseismic information derived from press reportsand published documents in Algeria, under certain conditions, is veryincomplete, even for destructive earthquakes, located in the countrysideaway from communication centres. One of the reasons for this iscensorship, noticeable during the colonisation period. Critical analysis ofnewly collected information has allowed the determination and/or theimprovement of the macroseismic parameters of each event, such aslocation, maximum epicentral intensity and magnitude to produce anearthquake catalogue as homogeneous and complete as the available data,for the zone under study. The criteria used in this research are explainedand eight historical earthquakes have been the subject of retrospectivemacroseismic field construction.The investigation of historical earthquakes is one of the most important taskin studying seismotectonic for seismic hazard evaluation purposes.     

An overview on the seismicity of Cuba

The seismicity of Cuba is briefly presented together with a few fundamental neotectonic elements of the adjacent Caribbean region. The Cuban seismicity catalogue has been extended back to 1528 and it shows that the largest earthquakes occurred in 1766 and 1852 (I = IX MSK). Two types of seismicity (intraplate and interplate) can be distinguished in Cuba. Western and Eastern Seismotectonic Units correspond to intraplate type and the Southeastern Seismotectonic Unit to interplate type. Western Cuba is characterized by a low frequency of earthquake occurrence. Distribution of epicenters is not regular and the most important events mainly concentrate along two regional active fault system (Nortecubana and Surcubana). Due to the lack of seismic stations in this region, the characterization of seismicity is frequently done on the grounds of historical data available from 1693. The main seismogenic source for Cuba is the Bartlett-Cayman fault system, but inland there are other active structures. Some issues about historical and present day Cuban seismological research are also showed.     

Probabilistic PGA and Arias Intensity maps of Kyrgyzstan (Central Asia)

New probabilistic seismic hazard and Arias Intensity maps have beendeveloped for the territory of the Kyrgyz Republic and bordering regions.Data were mainly taken from the seismic catalogue of Kyrgyzstan and partlyfrom the world seismic catalogue. On the base of seismicity and activetectonics, seismic zones were outlined over the area. For these,Gutenberg-Richter laws were defined using mainly instrumental data, butregarding also historical events. Attenuation of acceleration inside the targetarea could not be determined experimentally since existing strong motiondata are insufficient. Therefore, empirical laws defined for other territories,principally Europe and China, were applied to the present hazardcomputations. Final maps were calculated with the SEISRISKIII programaccording to EUROCODE8 criteria, i.e. for a period of 50 years with90% probability of non-exceedance. For long-term prediction, 100 yearsmaps with 90% probability of non-exceedance have been developed. Theprocedure used for seismic hazard prediction in terms of PGA (PeakGround Acceleration) was also applied to Arias intensities in order to beable to define regional seismogenic landslide hazard maps.