Deep medium environment of strong earthquakes occurrence in Yunnan region

The deep structure background of earth medium for strong earthquakes ccurrence in Yunnan area is discussed inthis paper, by using the results on the study of the velocity structure, elect fieal conductivity stricture, geothermalstructure in the crust and upper mantle in Yunnan area. The results show that the occurrence of strong earthquakes in Yunnan region is obviously related to the deep medium and tectonic environment such as the existenceof the high velocity zone in the upper crust, the low velocity zone or high electrical conductivity layer in themiddle crust, local uplift in the upper mantle, high geothermal activity and deep and large fault, etc. The large earthquakes could not take place at anywhere, they often occur at some regions which have a certainbackground in the deep medium structure. The activity of the earthquakes with magnitude of 5 or less is quite random,the occurrence of them have not the obvious background of the deep medium strUcture.

Deep and Ultra-Deep Earthquakes Worldwide, Possible Anomalies in South America

The aim of this paper is to evaluate the worldwide variation of deep and ultra-deep earthquakes (DQ and UDQ) during the period 1996-2017. This project found only three locations around the globe presenting this kind of seismicity. Although there are other global settings showing deep seismicity, they are not periodical and cannot be considered by a statistical view. The three areas with intense activity for DQ and UDQ events are located mostly in subduction areas. The largest variations of DQ and UDQ border the Pacific Ocean and include the North Pacific, South Pacific, and South America. The major difference in this set is that the first two sites are subduction zones and the South American occurrences happened in the interior of the continent. Another anomaly is an internal layer between 300 - 500 km in South America that shows no tremors in the period studied. However, below 500 km activity reappears, even at extreme depths of up to 650 km. We suggested that the reason for those occurrences would be due to an anomaly in the asthenosphere in this region. This anomaly would probably be presenting a breakable material that was pushed by the Nazca platform against the South America plate. Other depths below 100 km in all the regions are discussed as well. We suggested that the reason for those occurrences was an anomaly created in the asthenosphere as part of the process of the South America collision with the Nazca plate. Part of the Nazca plate has subducted below South America, creating a slab as deep as 500 km. The convergent slab is still moving against South America and sinking due to the gravity and rotation of the Earth. The discrepancies in the occurrences we tracked at different locations indicated that this slab had different thicknesses around South America. We found similar results for Vanuatu and Fiji;in these regions UDQ events occur at the subduction zones under the ocean with depths greater than 700 km. Here, a possible explanation is that part of the lithosphere is subducted at these depths and is causing tremors.

The accurate location of the injection- induced microearthquakes in German Continental Deep Drilling Program

From August 21, 2000 to October 20, 2000,a fluid injection-induced seismicity experiment has been carried out in the KTB (German Continental Deep Drilling Program). The KTB seismic network recorded more than 2 700 events. Among them 237 events were of high signal-to-noise ratio, and were processed and accurately located. When the events were located, non KTB events were weeded out by Wadatis method. The standard deviation, mean and median were obtained by Jackknife's technique, and finally the events were accurately located by Gei-gers method so that the mean error is about 0.1 km. No earthquakes with focal depth greater than 9.3 km, which is nearly at the bottom of the hole, were detected. One of the explanation is that at such depths the stress levels may not close to the rocks frictional strength so that failure could not be induced by the relatively small perturbation in pore pressure. Or at these depths there may be no permeable, well-oriented faults. This depth may be in close proximity to the bottom of the hole to the brittle-ductile transition, even in this relatively stable interior of the in-teraplate. This phenomenon is explained by the experimental results and geothermal data from the superdeep bore-hole.

Recent Advances of Deep Learning in Geological Hazard Forecasting

Geological hazard is an adverse geological condition that can cause loss of life and property.Accurate prediction and analysis of geological hazards is an important and challenging task.In the past decade,there has been a great expansion of geohazard detection data and advancement in data-driven simulation techniques.In particular,great efforts have been made in applying deep learning to predict geohazards.To understand the recent progress in this field,this paper provides an overview of the commonly used data sources and deep neural networks in the prediction of a variety of geological hazards.

Deep structural characteristics and seismogenesis of the M≥8.0 earthquakes in North China

Based on the results from seismogeological study, aeromagnetic inversion and deep seismic sounding (DSS), it is found that the M8.0 earthquakes in North China have three common deep structural characteristics, i.e., they all took place above the ultra-crustal deep faults or on the edges of the tectonic blocks with higher intensity, and there are low-velocity, low-density and high-conductive layers deep in the epicentral regions. The origins of the earth-quakes are also discussed and the two possibilities of seismogenesis are proposed, i.e., tectonic movement and intracrustal explosion.

Effects of mining－induced earthquakes on water table in deep wells

Based on the systematical collection and processing of data on the influence of mining-induced earthquakes on water table regime in deep well Lu-15 in Taozhuang Coal Mine since 1980, we study the characteristics of coseismic effect of water table in deep well in this paper. We have found precursory phenomena of water table in deep well before mining-induced earthquake. Here we discuss the physical mechanism of coseismic effect of mining--induced earthquake on water table in deep well.

Investigation of Relation between Solar Activity and Earthquakes with Deep Learning Method

Solar activity (SA) has been hypothesized to be a trigger of earthquakes, although it is not as intuitively associated as other potential triggers such as tidal stress, rainfall, and the building of artificial water reservoirs. Here, we investigate the relation between SA and global earthquake numbers (GEN) by using a deep learning method to test the hypothesis. We use the daily data of GEN and SA (1996/01/01-2019/12/31) to construct a temporal convolution network (TCN). From the computational results, we confirm that the TCN captures the relation between SA and earthquakes with magnitudes from 4.0 to 4.9. We also find that the TCN achieves better fitting and prediction performance compared with previous work.

Anomalously deep earthquakes related to the Ojo de Agua Lineament and its tectonic significance,Sierras Pampeanas of Córdoba,Central Argentina

The Sierras de Cordoba are the easternmost uplifted ranges of the Sierras Pampeanas geological province of Argentina. They are composed of a Neoproterozoic-Paleozoic basement arranged in north-south aligned mountain ranges, limited by west-vergent reverse faults, reactivated or formed by compressive tectonics during the Andean orogeny. The ranges are also affected by oblique subvertical lineaments,probably related to pan-Gondwanan structures. The recorded seismicity shows anomalously deep earthquakes（up to 80 km depth） concentrated in the northwestern area. We attribute this seismicity to the current tectonic activity of the Ojo de Agua Lineament. This lineament is a N13°-135° strike, 70°-80° NE dip,macrostructure with more than 80 km depth and 160 km length. A sinistral transcompressional kinematics（convergent oblique shear） is deduced by the focal mechanism of a deep earthquake, together with hydrological and geomorphological features strongly modified. The continental lithosphere under the Sierras de Cordoba would be colder and more rigid than in a normal subduction area, due to the retraction of the asthenospheric wedge to the foreland, causing seismicity to depths greater than 40 km, below the Mohorovicic discontinuity. Neogene volcanism would be closely related to this lineament, allowing the rapid ascent of melts from the mantle.

Seasonality and Tectonic Influences on Subduction Zones for Ultra-Deep Earthquakes

Our previous research has found that deep or very deep earthquakes can be influenced by different seasons of the year. It also indicates that other factors may impact the seasonality in addition to these external parameters. This would explain why the response from Northern Hemisphere and Southern Hemisphere for the seasons is different. In the current research, we will focus on very deep earthquakes over a very long period, 1950-2017, which have high magnitude of M ≥ 6 with depth ≥ 500 km and named ultra-deep earthquakes (UDQ). We will separate such events by coordinates of each subduction area located in the Pacific Ring of Fire to find which effects the seasons have on these specific areas. Former tomographic studies in such regions pointed out that each area mentioned had systematic differences in the slab configuration along arcs. Our conclusions showed that those discrepancies may influence the enhancement of earthquakes in some seasons or months.

2018年9月8日墨江5.9级地震云南普洱大寨流体异常特征及机理

文中梳理了2004年以来普洱大寨井连续观测的水化学离子和井-含水层渗透性异常特征。研究发现,在观测井周边250km范围内5.5级以上地震发生前,多次出现过可重复、可类比的异常变化,对地震具有较好的异常指示和预测意义。但相比以往震例,墨江5.9级地震发生前,无论是化学离子还是物理参数均出现了观测以来幅度最大的变化,异常状态较以往强烈很多,但发震的震级只有5.9级。为了研究这一现象产生的原因和机理,文中尝试从区域深部物质活动和区域应力水平2个方面对墨江5.9级地震前的异常演化过程开展讨论,得到以下认识:墨江5.9级地震前,流体异常整体呈现出较为显著的从深部到浅部、从背景到短期微观异常再到临震宏观异常的演化过程;墨江5.9级地震前,普洱大寨连续观测的水化学离子浓度异常和井-含水层渗透性的改变是由于区域内垂向剪切应力持续增强引起的含水层受挤压,从而形成了垂向的流体补给,最终引起不同含水层水体发生交替混合而产生的结果;本次异常形成初期还伴随深部物质剧烈活动的现象,较为显著的由深部到浅部的耦合作用过程可能是导致墨江5.9级地震前出现自观测以来地下流体异常幅度最显著的原因。因此,流体活动从深部开始,随着区域应力不断积累,不断向地表传递的演变过程是墨江5.9级地震前流体异常演化的本质特征;区域应力的作用方式和深部物质活动程度不同,是引起墨江5.9级地震前异常特征与研究区其他历史震例前明显不同的根本原因。文中研究为全面认识普洱大寨井地下流体异常的预测意义和地震前流体异常的深浅耦合演化过程提供了一定参考。

基于三维剩余密度结构的松原地震成因

自2006年以来松原市乾安县与宁江区地震频发,成为东北地震活动最为频繁的区域,目前对两地的发震构造和地震成因的认识存在严重分歧,制约了地震危险性评价与预防工作的开展。文中通过对区域重力数据进行非线性共轭梯度聚焦反演,获得了松原震区的三维剩余密度结构,结合石油井震资料,获得了如下认识:1)研究区的剩余密度异常呈高低相间的带状分布,南部异常走向为NNW,北部异常转变为NNE向,该特征反映出乾安震区和宁江震区的深部孕震环境不同,前者震源位于查干花高密度异常体内及其边缘,后者震源位于松原低密度异常带中部,指示两地震源位置的岩性不同;2)两者的发震构造不相同,前者受控于查干花断裂和乾安断裂,后者受控于松原断裂和扶余北断裂;3)地震的形成与区域应力,基底结构,深部气、流体运移和长期油气开采等因素有关。长期注水采油破坏了地质结构和应力环境,可能是重要的地震诱发因素。

深度学习在地震监测预报中的应用进展

对深度学习的方法原理及主流的前馈神经网络、卷积神经网络、循环神经网络、Transformer网络、自编码器、生成对抗网络以及深度强化学习网络等进行了介绍,讨论了不同网络的适用领域。从震相拾取、震相关联、地震定位与事件检测,地震信号和地震事件的分类,地震预测预报等方面对近年来深度学习方法的应用技术进行了提炼总结,综述了深度学习方法的应用进展,讨论了当前常见深度学习方法在地震监测预报领域中的主要应用方式、优势特点及解决的主要问题。总结了现阶段深度学习方法在地震监测预报领域中存在的应用局限性以及后续发展方向。

深切V型峡谷物理驱动人工智能波动模拟

高山峡谷区场地地震效应是地震工程领域研究热点。V形峡谷引起的圆柱形SH波散射和衍射波函数的级数解已较为成熟,并为众多河谷区重大工程提供了合理、科学的地震动输入。采用物理驱动深度学习方法结合与解析结果的对比分析,近一步明确了V型河谷地形地震反应特性及复杂波场空间分布。此方法主要关注稀疏样本及可诠释性人工智能,结合强形式自动微分和软约束边界条件嵌入,建立深度神经网络实现半无限域地震传播模型。采用时间域分解策略,实现不同给定波场工况下V型河谷高精度预测。通过与解析解对比,评估了所提出的物理驱动人工智能方法的精度和效率。结果表明,物理驱动人工智能方法可应用于地形效应分析,柱面SH波在V型峡谷底端发生显著衰减与振荡,边缘区呈现放大效应。

巨厚弱胶结覆岩深部开采大能量事件与地表沉陷关系研究

陕蒙矿区是我国重要的煤矿开采基地,区域侏罗系煤层覆岩中普遍存在巨厚弱胶结覆岩,虽然覆岩岩性总体呈中硬偏软弱,但实测地表下沉相对较小,且伴随频繁的大能量事件发生,给工作面安全高效开采带来了较大安全隐患。为研究巨厚弱胶结覆岩深部开采大能量事件与地表沉陷的关系,对石拉乌素煤矿1203工作面与1208工作面进行了地表沉陷实测与矿震资料分析,获得了该地区地表移动变形规律和矿震数据,通过对比分析研究发现:巨厚弱胶结覆岩地表移动变形下沉分布集中,最大下沉处均位于工作面中部偏向已采工作面侧,整体地表下沉盆地形态及下沉增加过程与中东部相似,但在未达到充分采动时,西部巨厚弱胶结矿区地表下沉值相比中东部明显偏小;巨厚弱胶结矿区煤层回采过程中均存在微震事件的活跃期,该阶段微震事件的能量和次数较高,同时伴随着105 J≤E的大能量事件发生,105 J≤E的矿震事件虽然频次较低,但在能量释放上占据重要地位;弱胶结矿区地表沉陷与能量事件之间存在着关联性,随着工作面的推进,最大下沉值突变往往伴随着大能量事件的发生。

Step-over of strike-slip faults and overpressure fluid favor occurrence of foreshocks:Insights from the 1975 Haicheng fore-main-aftershock sequence,China

This study analyzed and summarized in detail the spatial and temporal distributions of earthquakes,tidal responses,focal mechanisms,and stress field characteristics for the M 7.3 Haicheng earthquake sequence in February 1975.The foreshocks are related to the main fault and the conjugate faults surrounding the extension step-over in the middle.The initiation timing of the foreshock clusters and the original time of the mainshock were clearly modulated by the Earth's tidal force and coincided with the peak of dilational volumetric tidal strain.As a plausible and testable hypothesis,we proposed a fluid-driven foreshock model,by which all observed seismicity features can be more reasonably interpreted with respect to the results of existing models.Together with some other known examples,the widely existing step-over along strike-slip faults and associated conjugate faults,especially for extensional ones in the presence of deep fluids,favor the occurrence of short-term foreshocks.Although clustered seismicity with characteristics similar to those of the studied case is not a sufficient and necessary condition for large earthquakes to occur under similar tectonic conditions,it undoubtedly has a warning significance for the criticality of the main fault.Subsequent testing would require quantification of true/false positives/negatives.

内蒙古测震台网实时智能地震处理系统运行实践——以2020年和林格尔地区地震事件为例

为评估实时智能地震处理系统(RISP)在内蒙古测震台网运行的可靠性,以2020年3月30日和林格尔ML 4.5地震前后30天内该区发生的31条地震事件为研究对象,将人工编目与实时智能地震处理系统产出结果(自动目录)进行对比分析,得出以下结论:RISP系统识别事件数量约为人工识别数量的2.5倍,其中自动目录有30条与人工目录(31条)相匹配,事件召回率高达96.8%;自动目录在发震时刻、震中位置、震级、P波和S波震相到时方面,与人工目录偏差较小。由自动目录与人工目录结果对比可知,2种目录相同事件的编目结果基本保持一致,震中偏差一般在±10 km范围内,发震时刻一般在±2 s范围内,自动目录基本符合人工编目误差范围要求。综合来看,实时智能地震处理系统(RISP)产出结果符合预期目标,可为震后快速产出余震序列、震群趋势判断等相关科学研究提供数据支撑。

Operation practice of real-time intelligent seismic processing system for the Nei Monggol seismic network——Taking the 2020 Helinger earthquake event as an example

To evaluate the reliability of the Real-time Intelligent Seismic Processing System(RISP)in the operation of the Nei Monggol seismic network,31 earthquake events occurred in the area within 30 days before and after the Helinger ML 4.5 earthquake that occurred on March 30,2020,were taken as the research object.The results of manual cataloging and real-time intelligent seismic processing system output(automatic cataloging)were compared and analyzed,and the following conclusions were drawn:The number of events identified by the real-time intelligent seismic processing system(RISP)is about 2.5 times that of manual identification.The automatic catalog matches 30 events from the manual catalog,and the event recall rate is as high as 96.8%.The automatic catalog has a smaller deviation from the manual catalog in terms of the time of earthquake occurrence,epicenter position,magnitude,and P and S phase arrivals.By comparing the results of automatic and manual catalogs,it can be seen that the cataloging results for the same event in both catalogs are consistent,with an epicenter deviation generally within the range of±10 km and an earthquake occurrence time generally within the range of±2 s.The automatic catalog basically meets the requirements of the error range for manual cataloging.Overall,the output results of the Real-time Intelligent Earthquake Processing System(RISP)meet the expected goals and can provide data support for scientific research such as rapid post-earthquake aftershock sequences and earthquake swarm trend judgment.

基于深度学习的地震诱发滑坡自动提取研究

地震诱发滑坡的提取是震区工程风险评价的基础,对震区的灾后重建工作具有重要意义。传统的机器学习方法需要复杂的数据预处理及设计特征工程工作,而深度学习方法则可以直接输入图像数据进行端对端学习,从而实现对地震诱发滑坡的自动提取。本文探究了U-Net与LinkNet两种卷积神经网络在地震诱发滑坡自动提取任务中的应用。研究表明U-Net和LinkNet在地震诱发滑坡自动提取应用中具有巨大的潜力,召回系数、F1分数、精确度均达到0.8以上。相较之下,LinkNet网络结构在滑坡的自动提取任务中整体性能优于U-Net,召回系数、F1分数、精确度分别提升2.0%~8.0%、4.0%~8.0%、8.0%~10.0%。U-Net网络结构适用于简单背景图像中大型滑坡的提取,而LinkNet网络结构则更适用于复杂背景图像中的滑坡及简单背景图像中小型滑坡的提取。

Investigation of Potential Factors on South Atlantic Magnetic Anomaly

The first part of this investigation analyzes the deep earthquake occurrences in Nazca subducting under South America. The depth taken is to get information about possible influences from the unknown materials and formations under the crust. The results revealed the presence of malleable material, which is unbreakable and, therefore, unable to trigger earthquakes. The structure of those elements is diamagnetic, attracting ionized particles from the Van Allen belt region in the ionosphere. The charged particles travel towards Earth’s surface, enhanced during the geomagnetic storms. The South Atlantic Magnetic Anomaly (SAMA) found that the deformation suffered by the anomaly moving from South Africa to South America is, possibly due to a bulge of unknown flexible material buried underneath the oceanic and continental crust. The continental part is strengthening in weakness because the background also has a high amount of diamagnetic material in this region, and it would not happen over the Atlantic Ocean, where part of the deformation is placed.

Possible link between long-term and short-term water injections and earthquakes in salt mine and shale gas site in Changning,south Sichuan Basin, China

Late at night on 17 June 2019,a magnitude 6.0 earthquake struck Shuanghe Town and its surrounding area in Changning County,Sichuan,China,becoming the largest earthquake recorded within the southern Sichuan Basin.A series of earthquakes with magnitudes up to 5.6 occurred during a short period after the mainshock,and we thus refer to these earthquakes as the Changning M6 earthquake sequence(or swarm).The mainshock was located very close to a salt mine,into which for^3 decades fresh water had been extensively injected through several wells at a depth of 2.7–3 km.It was also near(within^15 km)the epicenter of the 18 December 2018 M5.7 Xingwen earthquake,which is thought to have been induced by shale gas hydraulic fracturing(HF),prompting questions about the possible involvement of industrial activities in the M6 sequence.Following previous studies,this paper focuses on the relationship between injection and seismicity in the Shuanghe salt field and its adjacent Shangluo shale gas block.Except for a period of serious water loss after the start of cross-well injection in 2005–2006,the frequency of earthquakes shows a slightly increasing tendency.Overall,there is a good correlation between the event rate in the Shuanghe area and the loss of injected water.More than 400 M≥3 earthquakes,including 40 M≥4 and 5 M≥5 events,had been observed by the end of August 2019.Meanwhile,in the Shangluo area,seismicity has increased during drilling and HF operations(mostly in vertical wells)since about 2009,and dramatically since the end of 2014,coincident with the start of systematic HF in the area.The event rate shows a progressively increasing background with some fluctuations,paralleling the increase in HF operations.More than 700 M≥3 earthquakes,including 10 M≥4 and 3 M≥5 in spatially and temporally clustered seismic events,are correlated closely with active fracturing platforms.Well-resolved centroid moment tensor results for M≥4 earthquakes were shown to occur at very shallow depths around shale formations with active HF,in agreement with some of the clusters,which occurred within the coverage area of temporary or new permanent monitoring stations and thus have been precisely located.After the Xingwen M5.7 earthquake,seismic activity in the salt well area increased significantly.The Xingwen earthquake may have created a unidirectional rupture to the NNW,with an end point close to the NW-trending fault of the Shuanghe earthquake.Thus,a fault in the Changning anticline might have terminated the fault rupture of the Xingwen earthquake,possibly giving the Xingwen earthquake a role in promoting the Changning M6 event.