Geological setting of the 8 October 2005 Kashmir earthquake

The source of the 8 October 2005 earthquake of M 7.6 was the northwest-striking Balakot–Bagh (B–B) fault, which had been mapped by the Geological Survey of Pakistan prior to the earthquake but had not been recognized as active except for a 16-km section near Muzaffarabad. The fault follows the Indus–Kohistan Seismic Zone (IKSZ); both cut across and locally offset the Hazara–Kashmir Syntaxis defined by the Main Boundary and Panjal thrusts. The fault has no expression in facies of the Miocene–Pleistocene Siwalik Group but does offset late Pleistocene terrace surfaces in Pakistan-administered Jammu-Kashmir. Two en-échelon anticlines near Muzaffarabad and Balakot expose Precambrian Muzaffarabad Limestone and are cut by the B–B fault on their southwest sides, suggesting that folding and exposure of Precambrian rocks by erosion accompanied Quaternary displacement along the fault. The B–B fault has reverse separation, northeast side up; uplift of the northeast side accompanied displacement, producing higher topography and steeper stream gradients northeast of the fault. No surface expression of the B–B fault has been found northwest of the syntaxis, although the IKSZ and steeper stream gradients continue at least as far as the Indus River, the site of the Pattan earthquake of M 6.2 in 1974. To the southeast, northwest-striking faults were mapped by the Geological Survey of Pakistan. One of these faults, the Riasi thrust, cuts across the southwest flank of an anticline exposing Precambrian limestone. Farther southeast, in Indian-administered territory, Holocene activity on the Riasi thrust has been described. In the Kangra reentrant still farther southeast, active faulting may follow the Soan thrust, along which Holocene and Pleistocene offsets have been described. The Soan thrust, rather than the south flank of the Janauri anticline, may represent the surface projection of the 1905 Kangra earthquake of M 7.8.     

A seismic gap on the Anninghe fault in western Sichuan,China

Through integrated analyses of time-varying patterns of regional seismicity, occurrence background of strong and large historical earthquakes along active faults, and temporal-spatial distribution of accu- rately relocated hypocenters of modern small earthquakes, this paper analyzes and discusses the im- plication of a 30-year-lasting seismic quiescence in the region along and surrounding the Anninghe and Zemuhe faults in western Sichuan, China. It suggests that the seismic quiescence for ML≥4.0 events has been lasting in the studied region since January, 1977, along with the formation and evaluation of a seismic gap of the second kind, the Anninghe seismic gap. The Anninghe seismic gap has the background of a seismic gap of the first kind along the Anninghe fault, and has resulted from evident fault-locking and strain-accumulating along the fault during the last 30 years. Now, two fault sections either without or with less small earthquakes exist along the Anninghe fault within the An- ninghe seismic gap. They indicate two linked and locked fault-sections, the northern Mianning section and the Mianning-Xichang section with lengths of 65 km and 75 km and elapsed time from the latest large earthquakes of 527 and 471 years, respectively. Along the Anninghe fault, characteristics of both the background of the first kind seismic gap and the seismicity patterns of the second seismic gap, as well as the hypocenter depth distribution of modern small earthquakes are comparable, respectively, to those appearing before the M=8.1 Hoh Xil earthquake of 2001 and to those emerging in the 20 years before the M=7.1 Loma Prieta, California, earthquake of 1989, suggesting that the Anninghe seismic gap is tending to become mature, and hence its mid- to long-term potential of large earthquakes should be noticeable. The probable maximum magnitudes of the potential earthquakes are estimated to be as large as 7.4 for both the two locked sections of the Anninghe fault.     

An Overview of the 28 October 2012 M<Subscript>w</Subscript> 7.7 Earthquake in Haida Gwaii,Canada: A Tsunamigenic Thrust Event Along a Predominantly Strike-Slip Margin

The boundary between the Pacific and North America plates along Canada’s west coast is one of the most seismically active regions of Canada, and is where Canada’s two largest instrumentally recorded earthquakes have occurred. Although this is a predominantly strike-slip transform fault boundary, there is a component of oblique convergence between the Pacific and North America plates off Haida Gwaii. The 2012 M_w 7.7 Haida Gwaii earthquake was a thrust event that generated a tsunami with significant run up of over 7 m in several inlets on the west coast of Moresby Island (several over 6 m, with a maximum of 13 m). Damage from this earthquake and tsunami was minor due to the lack of population and vulnerable structures on this coast.     

Areal Distribution of Ground Effects Induced by Strong Earthquakes in the Southern Apennines (Italy)

Moderate to strong crustal earthquakes are generally accompanied by a distinctivepattern of coseismic geological phenomena, ranging from surface faulting to groundcracks, landslides, liquefaction/compaction, which leave a permanent mark in thelandscape. Therefore, the repetition of surface faulting earthquakes over a geologictime interval determines a characteristic morphology closely related to seismic potential. To support this statement, the areal distribution and dimensions of effects of recent historical earthquakes in the Southern Apennines are being investigated in detail. This paper presents results concerning the 26 July 1805 earthquake in the Molise region, (I = X MCS, M = 6.8), and the 23 November 1980 earthquake in the Campania and Basilicata regions (I = X MSK, M_s = 6.9). Landslide data are also compared with two other historical earthquakes in the same region with similar macroseismic intensity. The number of significant effects (either ground deformation or hydrological anomalies) versus their minimum distance from the causative fault have been statistically analyzed, finding characteristic relationships. In particular, the decay of the number of landslides with distance from fault follows an exponential law, whereas it shows almost a rectilinear trend for liquefaction and hydrological anomalies. Most effects fall within the macroseismic area, landslides within intensity V to VI, liquefaction effects within VI and hydrologicalanomalies within IV MCS/MSK, hence at much larger distances. A possible correlation between maximum distance of effects and length of the reactivated fault zone is also noted. Maximum distances fit the envelope curves for Intensity and Magnitude based on worldwide data. These results suggest that a careful examination of coseismic geological effects can be important for a proper estimation of earthquake parameters and vulnerability of the natural environment for seismic hazard evaluation purposes.     

Coseismic deformation of the 2021 MW7.4 Maduo earthquake from joint inversion of InSAR,GPS, and teleseismic data

The M_W7.4 Maduo earthquake occurred on 22 May 2021 at 02:04 CST with a large-expansion surface rupture. This earthquake was located in the Bayan Har block at the eastern Tibetan Plateau, where eight earthquakes of M_S >7.0 have occurred in the past 25 years. Here, we combined interferometric synthetic aperture radar, GPS, and teleseismic data to study the coseismic slip distribution, fault geometry, and dynamic source rupture process of the Maduo earthquake. We found that the overall coseismic deformation field of the Maduo earthquake is distributed in the NWW-SEE direction along 285°. There was slight bending at the western end and two branches at the eastern end. The maximum slip is located near the eastern bending area on the northern branch of the fault system. The rupture nucleated on the Jiangcuo fault and propagated approximately 160 km along-strike in both the NWW and SEE directions. The characteristic source rupture process of the Maduo earthquake is similar to that of the 2010 M_W6.8 Yushu earthquake, indicating that similar earthquakes with large-expansion surface ruptures and small shallow slip deficits can occur on both the internal fault and boundary fault of the Bayan Har block.     

The rupture process and asperity distribution of three great earthquakes from long-period diffracted P-waves

Maximum earthquake size varies considerably amongst the subduction zones. This has been interpreted as a variation in the seismic coupling, which is presumably related to the mechanical conditions of the fault zone. The rupture process of a great earthquake indicates the distribution of strong (asperities) and weak regions of the fault. The rupture process of three great earthquakes (1963 Kurile Islands, M_W = 8.5; 1965 Rat Islands, M_W = 8.7; 1964 Alaska, M_W = 9.2) are studied by using WWSSN stations in the core shadow zone. Diffraction around the core attenuates the P-wave amplitudes such that on-scale long-period P-waves are recorded. There are striking differences between the seismograms of the great earthquakes; the Alaskan earthquake has the largest amplitude and a very long-period nature, while the Kurile Islands earthquake appears to be a sequence of magnitude 7.5 events.The source time functions are deconvolved from the observed records. The Kurile Islands rupture process is characterized by the breaking of asperities with a length scale of 40–60 km, and for the Alaskan earthquake the dominant length scale in the epicentral region is 140–200 km. The variation of length scale and M_W suggests that larger asperities cause larger earthquakes. The source time function of the 1979 Colombia earthquake (M_W = 8.3) is also deconvolved. This earthquake is characterized by a single asperity of length scale 100–120 km, which is consistent with the above pattern, as the Colombia subduction zone was previously ruptured by a great (M_W = 8.8) earthquake in 1906.The main result is that maximum earthquake size is related to the asperity distribution on the fault. The subduction zones with the largest earthquakes have very large asperities (e.g. the Alaskan earthquake), while the zones with the smaller great earthquakes (e.g. Kurile Islands) have smaller scattered asperities.     

Relocation of the MS5.7 Earthquake Sequence in Songyuan, Jilin Province, 2018 and the Analysis of Its Seismogenic Structure

The 2018,Songyuan,Jilin M_S5. 7 earthquake occurred at the intersection of the FuyuZhaodong fault and the Second Songhua River fault. The moment magnitude of this earthquake is M_W5. 3,the centroid depth by the waveform fitting is 12 km,and it is a strike-slip type event. In this paper,with the seismic phase data provided by the China Earthquake Network, the double-difference location method is used to relocate the earthquake sequence,finally the relocation results of 60 earthquakes are obtained. The results show that the aftershock zone is about 4. 3km long and 3. 1km wide,which is distributed in the NE direction. The depth distribution of the seismic sequence is 9km-10 km. 1-2 days after the main shock,the aftershocks were scattered throughout the aftershock zone,and the largest aftershock occurred in the northeastern part of the aftershock zone. After 3-8 days,the aftershocks mainly occurred in the southwestern part of the aftershock zone. The profile distribution of the earthquake sequence shows that the fault plane dips to the southeast with the dip angle of about 75°. Combined with the regional tectonic setting,focal mechanism solution and intensity distribution,we conclude that the concealed fault of the Fuyu-Zhaodong fault is the seismogenic fault of the Songyuan M_S5. 7 earthquake. This paper also relocates the earthquake sequence of the previous magnitude 5. 0 earthquake in 2017. Combined with the results of the focal mechanism solution,we believe that the two earthquakes have the same seismogenic structure,and the earthquake sequence generally develops to the southwest. The historical seismic activity since 2009 shows that after the magnitude 5. 0 earthquake in 2017,the frequency and intensity of earthquakes in the earthquake zone are obviously enhanced,and attention should be paid to the development of seismic activity in the southwest direction of the earthquake zone.     

Earthquake probabilities and magnitude distribution (<Emphasis Type="Italic">M</Emphasis>≥6.7) along the Haiyuan fault,northwestern China

In recent years, some researchers have studied the paleoearthquake along the Haiyuan fault and revealed a lot of paleoearthquake events. All available information allows more reliable analysis of earthquake recurrence interval and earthquake rupture patterns along the Haiyuan fault. Based on this paleoseismological information, the recurrence probability and magnitude distribution for M≥6.7 earthquakes in future 100 years along the Haiyuan fault can be obtained through weighted computation by using Poisson and Brownian passage time models and considering different rupture patterns. The result shows that the recurrence probability of M _S≥6.7 earthquakes is about 0.035 in future 100 years along the Haiyuan fault.     

The Beni-Ourtilane-Tachaouaft fault and Seismotectonic aspects of the Babors region (NE of Algeria)

A shallow moderate (M _s=5.7) but damaging earthquake shook theregion of Beni-Ourtilane located about 50 km NW of Setif and 390 kmNE of Algiers (Central Eastern Algeria). The main shock caused the deathof 2 peoples, injured 50 and caused sustainable damage to about 3000housing units. The main shock was preceded by 2 foreshocks and followedby many aftershocks which lasted for many days. Analysis of historicalseismicity including the localisation of epicenters, the trend of isoseismalmaps of some historical events, the localisation of the November 10, 2000main shock (M _s=5.7) and the November 16, 2000 aftershock(M _s=4.5) as well as the shape of the area of maximum intensity ofthe November 10, 2000 earthquake suggest that the Tachaouaft fault of20 km of length is the activated geological structure. Although, there isno clear surface breaks associated with this earthquake, the localisation ofgeological disorders, such as ground fissures, during the Beni-Ourtilaneearthquake, which are remarkably located near the fault, may have atectonic meaning. Geomorphological analysis through Digital ElevationModels (DEMs) allowed us to identify a clear fault scarp related likely tostrong earthquakes occurred in the past. Among geomorphologicalevidences of this active fault there are the uplift and tilt of alluvial terraceson the hanging wall and the diversion of the drainage pattern. Based onthe quality of constructions and field observations an intensity I ₀ = VII (MSK scale) is attributed to the epicentral area,which is striking NE-SW in agreement with the focal mechanism solutionand the seismotectonic observations. In the other hand the amount ofdamage is due rather to the bad quality of constructions than to theseverity of ground motion. The Tachaouaft fault with the Kherrata fault isthe main source of seismic hazard in the Babors region.     

四川长宁地区地震震源参数的时空分布特征

使用谱比法计算得到四川长宁地区2018年12月至2019年7月期间442个地震的震源参数,并进一步分析了震源参数之间的相互关系及应力降的时空分布特征.研究区的地震活动主要集中在长宁背斜核部和南部建武向斜页岩气开采区.研究结果显示,该地区ML1.3～4.7地震的应力降位于0.02～7.26MPa范围内,超过90％的地震应...     

2018年9月4日新疆伽师MS5.5地震序列及发震构造讨论

2018年9月4日新疆伽师发生M_S5.5地震,震中处于塔里木地块西北缘,位于1997~1998年伽师强震群震区内。此次伽师地震前发生了M_S4.7前震,截至9月30日最大余震震级为M_S4.6（M_L5.0）,初步判定为前-主-余型地震序列。序列精定位结果显示,余震沿近NE向展布,主震震源深度与1997~1998年伽师强震主震基本一致,发震断层陡立。本文从区域的构造环境、地震震源机制解和余震分布特征等方面分析认为,地震发生在伽师隐伏断裂东南端部,为1997~1998年伽师强震群震区的一次新的构造活动。序列参数、视应力等计算结果显示,伽师M_S5.5地震的预测最大余震震级与最大余震震级M_S4.6接近,表明序列最大余震已经发生。     

Geodynamic and Seismotectonic Activity in Eastern Tibet in the 21st Century

At the beginning of the 21st century, a series of great earthquakes were recorded in northeastern Tibet, along the periphery of the Bayan Hara lithospheric block. An earthquake with M_S = 8.1 occurred within the East Kunlun fault zone in the Kunlun Mountains, which caused an extended surface rupture with left-lateral strike slip. An earthquake with M_S = 8 occurred in Wenchuan (China) on May 12, 2008, giving rise to an extended overthrust along the Lunmanshan fault zone. An earthquake with M_S = 7.1 occurred in Yushu (China) on April 14, 2010; its epicenter was on the Grazze–Yushu–Funchuoshan fault; a left-lateral strikeslip offset was observed on the surface. An earthquake with M_S = 7 occurred in the vicinity of Lushan on April 20, 2013; its epicenter was within the Lunmanshan fault zone, 103 km southwest of the zone of the catastrophic Wenchuan earthquake. An earthquake with M_S = 8.2 occurred in Nepal on April 25, 2015. Based on the CSN seismic catalog, the energy of all earthquakes in eastern Tibet at the end of the 20th and beginning of the 21st centuries was estimated. It was found that Tibet was seismically quiet from 1980 to 2000. The beginning of the 21st century has been marked by seismic activation with earthquake sources migrating southward to surround the Bayan Hara lithospheric block from every quarter. Therefore, this block can be regarded as one of the most seismically active regions of China.     

Paleoseismic study of the Kamishiro Fault on the northern segment of the Itoigawa–Shizuoka Tectonic Line,Japan

The M_w 6.2 (Mj 6.8) Nagano (Japan) earthquake of 22 November 2014 produced a 9.3-km long surface rupture zone with a thrust-dominated displacement of up to 1.5 m, which duplicated the pre-existing Kamishiro Fault along the Itoigawa–Shizuoka Tectonic Line (ISTL), the plate-boundary between the Eurasian and North American plates, northern Nagano Prefecture, central Japan. To characterize the activity of the seismogenic fault zone, we conducted a paleoseismic study of the Kamishiro Fault. Field investigations and trench excavations revealed that seven morphogenic paleohistorical earthquakes (E2–E8) prior to the 2014 M_w 6.2 Nagano earthquake (E1) have occurred on the Kamishiro Fault during the last ca. 6000 years. Three of these events (E2–E4) are well constrained and correspond to historical earthquakes occurring in the last ca. 1200 years. This suggests an average recurrence interval of ca. 300–400 years on the seismogenic fault of the 2014 Kamishiro earthquake in the past 1200 years. The most recent event prior to the 2014 earthquakes (E1) is E2 and the penultimate and antepenultimate faulting events are E3 and E4, respectively. The penultimate faulting event (E3) occurred during the period of AD 1800–1400 and is associated with the 1791 M_w 6.8 earthquake. The antepenultimate faulting event (E4) is inferred to have occurred during the period of ca. AD 1000–700, likely corresponding to the AD 841 M_w 6.5 earthquake. The oldest faulting event (E8) in the study area is thought to have occurred during the period of ca. 5600–6000 years. The throw rate during the early Holocene is estimated to be 1.2–3.3 mm/a (average, 2.2 mm/a) with an average amount of characteristic offset of 0.7–1.1 m produced by individual event. When compared with active intraplate faults on Honshu Island, Japan, these slip rates and recurrence interval estimated for morphogenic earthquakes on the Kamishiro Fault along the ISTL appear high and short, respectively. This indicates that present activity on this fault is closely related to seismic faulting along the plate boundary between the Eurasian and North American plates.     

Radon Precursory Signals for Some Earthquakes of Magnitude > 5 Occurred in N-W Himalaya: An Overview

The N-W Himalaya was rocked by a few major and many minor earthquakes. Two major earthquakes in Garhwal Himalaya: Uttarkashi earthquake of magnitude M_s= 7.0 (m_b = 6.6) on October 20, 1991 in Bhagirthi valley and Chamoli earthquake of M_s= 6.5 (m_b = 6.8) on March 29, 1999 in the Alaknanda valley and one in Himachal Himalaya: Chamba earthquake of magnitude 5.1 on March 24, 1995 in Chamba region, were recorded during the last decade and correlated with radon anomalies. The helium anomaly for Chamoli earthquake was also recorded and the Helium/Radon ratio model was tested on it. The precursory nature of radon and helium anomalies is a strong indicator in favor of geochemical precursors for earthquake prediction and a preliminary test for the Helium/Radon ratio model.     

Tectonic and Kinematic Regime along the Northern Caribbean Plate Boundary: New Insights from Broad-band Modeling of the May 25, 1992, Ms = 6.9 Cabo Cruz, Cuba, Earthquake

—On May 25th, 1992, an M _s = 6.9 earthquake occurred off the southwestern tip of Cuba, along the boundary between the Caribbean and North American plates. This earthquake was the largest to strike southern Cuba since 1917 and the largest ever recorded in that region by global seismic networks. It is therefore a key element for our understanding of the tectonic and kinematic regime along the northern Caribbean plate boundary. In order to test the previously proposed source parameters of the Cabo Cruz earthquake and to better constrain its focal mechanism, we derived a new set of source parameters from unfiltered broad-band teleseismic records. We used a hybrid ray tracing method that allows us to take into account propagation effects of seismic waves in a realistic crustal model around the source. Our solution is consistent with the long-period focal mechanism solution of Virieux et al. (1992). Our solution also models the higher frequency crustal and water layer phases. The primarily strike-slip focal mechanism has a small thrust component. Its shows an east-west trending nodal plane dipping 55° to the north that we interpret as the rupture plane since it corresponds to the geometry of the major active fault in that area. The displacement on this plane is a left-lateral strike-slip combined with a small amount of southward thrust. The result is in good agreement with the active tectonic structures observed along the Oriente fault south of Cuba. The small thrust component demonstrates that, contrary to prior belief, the transpressive regime extends along this whole segment of the Caribbean/North American plate boundary. Together with historical seismicity, it suggests that most of the stress accumulated by the Caribbean/North American plate motion is released seismically along the southern Cuban margin during relatively few but large earthquakes.     

2013年山东莱州M4.6地震序列发震构造初探

采用双差定位法对山东莱州地震序列重新定位,通过CAP方法反演M4.6地震震源机制,在此基础上初步探讨莱州地震序列发震构造。结果显示:精确定位震中位置主要位于柞村—仙夼断裂的NW方向,深度剖面显示从SE方向到NW方向断层深度呈由浅逐渐变深的趋势,这均与柞村—仙夼断裂位置、走向、倾向特征较为吻合;M4.6地震震源机制解的节面Ⅰ与柞村—仙夼断裂走向、倾角较为接近。综合精确定位震中位置、剖面深度分布特征、M4.6地震震源机制解及宏观调查烈度分布等结果与柞村-仙夼断裂产状之间的关系,初步推测柞村—仙夼断裂可能为莱州地震序列的发震断层。     

2017年3月渤海地震序列微震检测与发震构造分析

地震序列发震构造研究是区域地震活动性和地震危险性分析的重要基础.2017年3月渤海海域发生地震序列活动,该序列发生在郯城-庐江断裂带与张家口-渤海地震带的交汇部位,区域构造较为复杂.然而在渤海海域,连续运行的固定地震监测仪器难以布设,导致地震监测能力相对较弱.本文首先采用模板匹配方法对序列遗漏地震进行检测,再使用波形互...     

中强地震前水氡短临异常的研究

本文根据对甘肃省及邻区近几年来发生的松潘7.2级强震、礼县5.0级中强震和海原5.5级中强震前水氡短临异常的分析研究,以及对多年来收集的50个中、强震例共139泉次水氡临震突变资料的分析研究,提出了有监视能力的水氡观测网点。若氡含量出现短趋势加速上升(或下降)和临震突变的同步异常则可能是发生中、强震的一个前兆信息。据此较好地试报了1982年6月8日武威4.1级地震。     

Stress interactions between normal faults and adjacent strike-slip faults of 1997 Jiashi earthquake swarm

During a 4-month period starting from 21 January, 1997, an earthquake swarm of seven major events (Ms≥6.0) struck the Jiashi region at the northwestern corner of the Tarim Basin in Xinjiang,, China. Previous relocation studies suggested that these strong earthquakes had occurred along at least two parallel rupture zones. According to the relocated hypocenters and focal mechanisms of the events, we have constructed fault models for these seven earthquakes to calculate the Coulomb stress changes produced by each of these events. Furthermore, we extended our model calculations to include an ad- jacent 1996 Ms=6.9 Artushi earthquake, which occurred one year before the Jiashi earthquake swarm. Our calculations show that the Coulomb stress change caused by the preceding events was around 0.05 MPa at the hypocenter of the 4th event, and higher than 0.08 MPa at the hypocenters of the 2nd, 3rd, 5th and 6th events. Our results reveal a Coulomb stress interactive cycle of earthquake triggering between two adjacent normal and strike-slip faults.