Research on the Tectonic Environment and Seismogenic Mechanism of the 1927 Gulang Great Earthquake with M=8.0

In this paper, we discussed the seismotectonic environment of the deep-seated and shallowcrust and seismological and geological model caused the 1927 Gulang great earthquake, basedon the recent research concerning about the active fault, surface rupture, fault planesolution, seismic activity, as well as the deep geophysical exploration data analysis in theepicentral area.The result shows that the 1927 Gulang great earthquake was caused by NE-SW-strikingcompressional thrusting. It was a latest event occurred in the reverse fault-folding belt thatdeveloped along the intracrustal decollement.     

对古浪8级大震孕育和发生的构造环境及发震模型的讨论

通过近年来对古良８级大震的震源机制解、震区活动构造、地震活动性及深部地球物理资料的研究,进一步探讨古良大震孕育和发生的、浅部地质构造环境和地震地质模型。研究结果认为,古浪地震是在北东－南西向挤压应力作用下,造山前陆逆断层沿深部低角度滑脱带产生逆冲－推覆运动形成的最新活动结果。     

Rupture Property of the 1927 Gulang Ms8.0 Earthquake and Numerical Simulation of Rupture Mechanism

INTRODUCTIONThe1927GulangMS8.0earthquake is a severe earthquake followed the HaiyuanMS8.5earthquake of1920inthe Qilian Mt._Hexi Corridor earthquake zone.The most severely hit region wasaround Gulang and Liangzhou(the present Wuwei)of Gansu Province,with a…     

Rupture Property of the 1927Gulang Ms8.0 Earthquake and Numerical Simulation of Rupture Mechanism1

The 1927 Gulang M_S8.0 earthquake is a severe earthquake that followed the Haiyuan M_S8.5 earthquake of 1920 in the Qilian Mt._Hexi Corridor earthquake zone. There are divergences of opinion in the previous studies about the rupture properties of the earthquake. Based on trenching and field investigation, and analysis of historical data, we hold that the earthquake resulted from the joint process of the Tianqiaogou_Huangyangchuan fault, Dongqingding segment of the Huangcheng_Shuangta fault and the Wuwei_Tianzhu buried fault, which constitute the Gulang nappe. By finite_element numerical simulation on the deformation mechanism of Gulang nappe, it is found that the stress and strain mainly concentrate in the western segment of the Tianqiaogou_Huangyangchuan fault, the Dongqingding segment of the Huangcheng_Shuangta fault, and the Gulangxia segment of the Wuwei_Tianzhu buried fault and the Gulang_Shuangta fault. The stress concentration coincides with the distribution of the earthquake surface rupture. It also proves that the earthquake is an outcome of the Gulang nappe activity as a whole.     

皇城—双塔断裂带的几何分段及运动学特征

在室内航,卫片解释及野外１：５万大比例尺活断层地质填图等专项研究的基础上,论证了１９２７年古浪８级大震主发震断裂皇城－双塔断裂带的几何分段及运动学特征。依据断层的几何特征,活动时期,活动强度可将该断裂带分为３段,分别为皇城盆地段（西段）、上寺段（中段）和冬青顶段（东段）。其中东段是古浪地震的发震段,与西段和中段相比,它具有活动时代新、活动强度大等特点,属全新世活动段。１９２７年古浪地震的发生与其特     

Spatial Distribution of Seismic Landslides in the Areas of 1927 Gulang M8.0 Earthquake

The 1927 Gulang M8.0 earthquake has triggered a huge number of landslides, resulting in massive loss of people''s life and property. However, integrated investigations and results regarding the landslides triggered by this earthquake are rare; such situation hinders the deep understanding of these landslides such as scale, extent, and distribution. With the support of Google Earth software, this study intends to finish the seismic landslides interpretation work in the areas of Gulang earthquake (VIII-XI degree) using the artificial visual interpretation method, and further analyze the spatial distribution and impact factors of these landslides. The results show that the earthquake has triggered at least 936 landslides in the VIII-XI degree zone, with a total landslide area of 58.6 km². The dense area of seismic landslides is located in the middle and southern parts of the X intensity circle. Statistical analysis shows that seismic landslides is mainly controlled by factors such as elevation, slope gradient, slope direction, strata, seismic intensity, faults and rivers. The elevation of 2 000-2 800 m is the high-incidence interval of the landslide. The landslide density is larger with a higher slope gradient. East and west directions are the dominant sliding directions. The areas with Cretaceous and Quaternary strata are the main areas of the Gulang seismic landslides. The X intensity zone triggered the most landslides. In addition, landslides often occur in regions near rivers and faults. This paper provides a scientific reference for exploring the development regularities of landslides triggered by the 1927 Gulang earthquake and effectively mitigating the landslide disasters of the earthquake.     

On Epicentral Location of the 1216 Mahu Earthquake in Leibo County, Sichuan Province

A query regarding the now commonly accepted epicentral location of the 1216 Mahu earthquake in Leibo County, Sichuan Province is proposed after examination of local historical records of earthquakes, field investigation of the Mahu barrier lake, study of geological environment for the earthquake and the available data then a relocation of the earthquake epicenter is suggested in the paper.     

6级左右历史地震震源参数的模拟估计

本文借鉴直接拟合烈度数据点和枚举震源参数的做法,设计了一种利用烈度资料估计6级左右历史地震震源参数的方法.该方法对震源参数所有可能的组合进行枚举,采用地震波场模拟计算转换的理论烈度值,利用模型选择方法评估各可能的震源参数组合模型与历史破坏记录推断的地震烈度数据点的拟合程度,对震源参数做出估计.该方法充分考虑到历史资料相对稀少对震源参数估计的影响,以多种震源参数估计结果和相应权重值来定量化表示估计的不确定性.通过对给定震中位置、震源深度和滑动角的Bootstrap数值恢复检测与2006年美国Parkfield 6.0级地震实例的测试,表明该方法得出的震源参数估计结果具有统计一致性和一定的无偏性.将该方法应用于1882年河北深县6级地震的震源参数估计,结果显示东西向旧城北断层或何庄断层及北东东走向的深西断层为深县地震的发震构造的可能性较大.     

Reappraised list of historical earthquakes that affected Israel and its close surroundings

Numerous historical reports of damaging earthquakes in the Levant have accumulated over the last 3000 years. Here, we screen that information and focus on the damaging earthquakes that affected Israel from the second millennia BCE to the 1927 CE Jericho earthquake and list the earthquakes by date, of major damage, type of sequence, and degree of size. The compilation results in three different lists: (i) 71 reliable earthquakes that in our opinion were most probably associated with the Dead Sea Transform (DST) and affected Israel and its close surroundings; (ii) 41 questionable earthquakes that should be re-evaluated or ignored; and (iii) 46 earthquakes that probably occurred but were erroneously associated with damage in Israel. What emerges from the list of the reliable earthquakes is that (i) Israel and its close surroundings suffered damage about 32 times during the last two millennia, that is, once in about 60 years, although not regularly; (ii) 21 of the earthquakes occurred during the last millennia, i.e., an event every ～45 years; and (iii) three intervals of increased reporting are noticed: between the fourth and the mid-eighth century, from the beginning of the eleventh to the end of the thirteenth century, and from the end of the eighteenth century up to the last entry in 1927, though this period may be extended until today. In-depth evaluation of the changing regimes over time within the study area, the historical reports of earthquake damage outside of Israel, and comparison with physical paleo- and archaeo-seismology evidence, such as the “137–206” and “165–236” paleoseismic earthquakes for which there is no historical match, indicates that the historical list is far from being complete. Thus, we argue that the apparent cycles of historical reporting do not necessarily reflect the actual rate of seismic activity and further investigation is needed to establish a compiled, multi-sourced list to decipher the true nature of cycles of strong earthquakes in this region during historical times.     

Recurrence pattern of Holocene earthquakes along the Dead Sea transform revealed by varve-counting and radiocarbon dating of lacustrine sediments

A high-resolution Holocene seismic history of the Dead Sea Transform (DST) is established from laminated sedimentary cores recovered at the shores of the Dead Sea. Radiocarbon dating and annual laminae counting yield excellent agreement between disturbed sedimentary structures (identified as seismites) and the historical earthquake record: All recent and historical strong events of the area were identified, including the major earthquakes of A.D. 1927, 1837, 1212, 1033, 749, and 31 B.C. The total of 53 seismites recognized along the entire Holocene profile indicate varying recurrence intervals of seismic activity between a few and 1000 years, with a conspicuous minimum rate at 2100-31 B.C. and a noticeable maximum during the past six to eight centuries. Most of the epicenters of the correlated earthquakes are situated very close to the Dead Sea (within 150 km) or up to 400 km north of it along the DST. Between 1000 B.C. and A.D. 1063, and from A.D. 1600 to recent time the epicenters are all located on the northern segment of the DST, whereas prior to 1000 B.C. and between A.D. 1000 and 1600 they appear to scatter along several segments of the DST. We establish how the local intensity exerts a control on the formation of seismites. At historically estimated intensities greater than VII, all well documented earthquakes are correlated, whereas at intensities smaller than VI none are matching.The periods with enhanced earthquake rate along the DST correlate with those along the North Anatolian Fault as opposed to the intervening East Anatolian Fault. This may indicate some elastic coupling on plate-boundary scale that may also underlie escape and extrusion tectonics, typical of continental collision.     

日本开发历史地震信息资源

阪神大震后,日本地震学界有计划有组织地开发历史地震信息资源,应用地震科学研究成果和最新科学技术与方法,在地震强震动、地震烈度、地震震级和区域构造特性等方面的研究取得进展,其成果已广泛应用于地震科学研究和地震防灾等方面。本文主要介绍日本地震学界开发历史地震信息资源的一些思路、做法和成果。     

古浪地震滑坡的分布规律和构造意义

１９２７年古浪地区发生了一次８级地震，地震时诱发了大量的滑坡和崩塌。本文根据野外调查和航片解译，分析了古浪地震滑坡的分布规律，探讨了古浪地震的地面破坏类型和滑坡滑动方向与区域构造应力场的关系。     

1927年古浪大震地质构造背景及其成因的初步探讨

本文根据多年野外考察资料,在论述1927年古浪大震形变带及发震断裂带特征基础上,分析了地震发生的地质构造背景,认为这次大震是塔儿庄—皇城断裂带和武威—天祝断裂带同时活动的产物,同时对两组断裂破裂方式进行了初步分析,提出了断块错动力学模型。     

青藏高原东北缘地震时空迁移的有限元数值模拟

地震在大陆内部断层系统中的时空迁移和丛集的基本力学机制一直是地球科学家关注的重要问题.青藏高原东北缘地震活动频繁,其地震时空迁移和地震丛集现象显著,是研究这个问题的重要区域.我们建立了一个三维黏弹塑性有限元模型,模拟了青藏高原东北缘主要活动断层系统的地震循环和地震时空迁移;计算了断层系统的应力演化;并探讨了断层之间的相互作用及地震时空迁移和地震丛集的原因.模拟结果显示断层之间的相互作用通过增加或降低断层上的库仑应力,加速或延缓了地震发生,使得区域地震可以在短时间内集中发生,从而形成地震丛集;另外,区域经过多个地震循环的长期演化,一些孕震断层上的应力状态恰好都达到屈服的临界状态附近,从而也可以导致这些断层上的地震在短期内集中发生,因此产生地震丛集和地震迁移.我们发现当区域经历地震丛集之后,该区域的应力大大释放,区域进入地震平静期;随着构造加载的持续,区域应力逐渐恢复,为下一次地震丛集或地震序列累积应力和能量;上述过程可以重复发生.因此地震丛集期与平静期交替出现.我们还统计了各个断层的大地震相互迁移的模拟结果,结果显示青藏高原东北缘下一次大地震有很大的概率会发生在海原断层上.     

2002年7月23日南黄海4.9级地震概述

概述了2002年7月23日南黄海Ms4.9地震的地震参数、地震影响、地震应急、地震预测，以及震源区地质构造及历史地震等情况。     

陕西地区流动重力历史资料清理分析

介绍流动重力历史资料清理流程、方法及获得的规范化成果,对1998年泾阳MS 4．8、2009年高陵MS 4．4地震前后的重力场变化进行分析,得到结论：①泾阳地震前后重力场变化满足“震前重力持续增强-震后反向恢复”的特征;②泾阳地震的发生可能与附近断裂活动有关,同时受华北块体应力场的作用;③高陵地震前后重力变化与泾阳地震前后重力变化具有一定的相似性,且位于渭河断裂附近,两个地震均受到渭河断裂活动的影响。     

海原断裂带刺儿沟古地震剖面炭屑~(14)C年龄及其意义

在青藏高原东北缘海原断裂带刺儿沟古地震剖面上不仅保存了地震活动的崩积楔遗迹,还发现多层炭屑以及与人类活动有关的铁渣、陶片等遗物,文中运用14C测年法和经红外释光照射后的绿光释光测年法(Post-IR OSL)分别对剖面上的炭屑、烘烤黏土、沉积物等样品进行年龄测定和比对,获得了各炭屑层和人类活动遗迹的年代。测定的人类活动遗迹年代与海原周缘历史记载的强震发生时间序列比对结果表明,刺儿沟人类活动遗迹的形成可能与历史地震无关,过去以炭屑年代作为地层年代来限定古地震发生的时代,建立的古地震事件时序的结果可能不正确,上述工作为进一步研究海原断裂带的强震复发规律和海原地区考古提供了重要的基础资料     

鲜水河断裂的几何形态对地震发生的影响

本文整理分析了鲜水河断裂的几何特征以及从1327年有记录以来6级以上历史地震的断层破裂位置和长度。选用速率和状态依赖性摩擦本构关系代表断裂区域物理性质,构建了鲜水河断裂3D物理模型模拟强震周期性。模拟结果与历史地震的发震有较好的一致性,主要表现在:1模拟结果在第二次地震周期之后,明显出现分段现象与鲜水河断裂分段的几何特征较为一致;2断裂北西端结构较为简单,地震发震情况也偏单一,在7级以上地震发震之前有6级以上地震的发生,此类现象与模拟结果一致;3断裂中段结构复杂,不仅存在分段还有轻度弯曲,模拟结果显示中段地震逐渐减小,破裂长度逐步缩短,并且出现级联破裂现象与历史地震较为吻合;43D模拟结果中,地震破裂区域起始与终止位置大都发生在断层转折的区域,特别是在乾宁和康定两处断层出现弯曲的位置,这与鲜水河断裂历史地震发震情况十分相似。     

DISCUSSION ON THE SEISMOGENIC STRUCTURE OF THE 2016 MENYUAN M6.4 EARTHQUAKE IN MENYUAN,QINGHAI

On January 21, 2016, a M6.4 earthquake occurred in Menyuan county, Qinghai Province. Its epicenter is located in the Qilian-Hexi Zoulang tectonic zone, which records several moderate-large historical earthquakes. Previous studies on this event are based on geology, remote sensing data and focal mechanism solutions, lacking analysis on its seismogenic structure. In order to study seismogenic fault plane and seismoteconic style of the earthquake, this work uses data of seismic intensity, aftershocks, and geology to address this issue. Furthermore, we calculate Coulomb stress changes imposed by the 1927 Gulang M8 and 1986 Menyuan M6.4 earthquake on the fault plane of the 2016 Menyuan M6.4 earthquake. The results indicate the early two events have posed distinct impacts on two nodal planes:loading or triggering on nodal plane Ⅰ, and unloading or delay on Ⅱ. In some cases such triggering stress is approaching or up to the threshold value of 0.01 MPa. Combining isoseismals, aftershock distribution, geological structure and different Coulomb stress changes aforementioned, the nodal plane Ⅱ of the source model is considered the seismogenic feature. In conjunction with geophysical data, we establish the seismogenic model of the Menyuan earthquake, which is a positive flower structure in a profile, gentle in the upper and steep in the lower, characterized by thrusting in a strike slipping fault system. This is a possible model for thrusting earthquakes generated by strike-slip faults in a compressional tectonic regime.     

2001年以来华亭小震活动增强现象的研究

通过对甘肃省平凉市华亭地区2001年以来出现的异常地震活动现象和该区矿产开采情况的相关分析和我国历史矿震资料的研究,得到了该地区出现的异常地震活动现象是由矿山开采引起的结论。对该地区的震情和震害做了预测并提出了防震减灾的建议。