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.

Characteristics of seismic activity before several large Sumatra, Indonesia, earthquakes

Two great earthquakes of MS8.5 and MS8.3 determined by the China Earthquake Networks Center (CENC) occurred successively on September 12 and 13, 2007 in the sea area to the south of Sumatra, which is another group of large earthquakes after MS8.7 event on December 26, 2004 and MS8.5 event on March 29, 2005. The

A tectonic stress map of China and adjacent regions from earthquakes occurred during 2000～2004

Earthquake focal mechanism solutions provide the basic information about the present-day regional tectonics stress distribution, which controls the activities of crustal faults. Therefore, continued efforts for updating the database of earthquake focal mechanism solutions are quite valuable and important.

The shock event of October 6,1597 is a strong deep earthquake

A special earth shock event was recorded at 22 counties of the 7 provinces of eastern China on October 6,1597,and 2 volcanic eruptions and seismic activities were recorded in Sanshui county,Xianjingbeidao,Korea atthat day and the 3rd day. Because of the large range of this shock,low intensity,slow attenuation and no extreme-earthquake area,its epicenter and focus could not be determined on the scientific-technological conditions at thattime,In the Seismological Catalogue of China(GU,1983)published in 1983,its epicenter was determined to be inthe Bo Sea(38.5°N,120.0°E),its magnitude was 7;and it was changed into 7.5 in the later Seismological Cata-

An examination of the presence and topography of the D'' discontinuity under the Russia–Kazakhstan border region using seismic waveform data from a deep earthquake in Spain

The D＇＇ layer,which is located atop the core–mantle boundary,has long been an area of focus for global seismology studies. A widely used approach to study the discontinuities in the D＇＇ layer involves the use of the SdS phases between the S and ScS phases,which requires that certain stringent conditions be satisfied with respect to an epicentral distance and earthquake depth. Therefore,this approach is only practical for investigating the presence and topography of velocity interfaces in certain local regions around the world. The Russia–Kazakhstan border region has been a ‘‘blind spot＇＇ with respect to this detection method. The seismic network deployed in the northeastern margin of the Tibetan Plateau has recorded relatively clear SdS phases for the MS6.3 earthquake that occurred in Spain on April 11,2010,allowing this blind spot to be studied. This paper compares the observed waveforms and synthetics and uses the travel times of the relevant phases to obtain a D＇＇ discontinuity depth between2,610 and 2,740 km in the examined area. This study provides the first results regarding the depth of the D＇＇ layer discontinuity for this region and represents an important addition to the global studies of the D＇＇ layer.

Geothermic activity and seismotectonics in the altitude of the Tibetan plateau

In the present analysis on the relationships among the depth of lithosphere brittle fracture, seismotectonics and geothermal anomalous active in Tibetan plateau were investigated using the seismic dada from ISC and Chinese seismic net and geothermal data. The results suggest that the region of anomalously geothermal activity almost coincides with that of the normal faulting type earthquake. The geothermal anomaly activity region coincides spatially with that of the events deeper than 60 km as well as. The normal faulting earthquakes may be mainly tectonic activity regimes until 110 km deep in the thermal anomaly region. The strike directions of events are likely the N-S direction, coinciding with the strike of the thermal anomaly active belts. The earthquakes align along the normal faults and faulted-depression zone with the N-S direction. The thermal anomaly activity also distributes along the faulted-depression zone. Many events deeper than 60 km exist in the anomalously geothermal activity region in the plateau. Events extend to bottom of the lithosphere of 110 km from the surface, like columnar seismic crowd. The lithosphere extends along the E-W direction due to the E-W extensional stress in the central and southern Tibetan plateau, altitude of the plateau. The t6nsional stress in the E-W results in the lithosphere fractures and the normal faults striking N-S direction, grabens and faulted-depression zones. Thermal material from the asthenosphere wells upward to the surface along deep seismic fractures and faults through the thick crust. The anomalously thermal activities are attributable to the upwelling thermal material from the mantle in the altitude of Tibetan plateau.

Characteristics of seismic activity before Chile M_W8.8 earthquake in 2010

The tempo-spatial variation of seismic activity before great Chile Mw8.8 earthquake on February 27, 2010 is studied. Some results are as follows： ①Two types of seismic gaps appeared before the Chile MwS.8 shock. One is background gap of Mw≥8.0 earthquakes with 360 km length since 1900, the other is seismogenic gap formed by M≥5.5 earth- quakes with 780km length five years before the Chile earthquake; ②There was only one Mw7.1 earthquake in the middle and southern part of Chile from 1986 to 2010. The obvious quiescence of Mw≥7.0 earthquake is the long-term background anomaly for the Chile earthquake; ③ The quiescence of M≥6.5 earthquakes appeared in South American block and its vicinity during the period from 2007 to 2009, and the quietude state has been disappeared three months before the Chile Mw8.8 earthquake; ④ The deep and intermediate-depth earthquake activity has been noticeablely strengthened in the subduction zone of South American block since 1993; ⑤The great Chile earthquake shows that global seismicity is still in the active period of Mw≥8.5 earthquakes since 2004. Based on the characteristics of the former two active periods, several great earthquakes with Mw≥8.5 would take place in a few years. In addition, the circum-Pacific seismic belt would be the main region for Mw≥8.0 earthquakes.

Pre-seismic gravity anomalies before Linkou Ms6.4 earthquake by continuous gravity observation of Crustal Movement Observation Network of China

A Ms6.4 earthquake occurred at Linkou country, Heilongjiang Province （44.8°N, 129.9°E） on January 2, 2016 at a depth of 580 km. Pre-seismic graviW anomalies obtained at a 1 Hz sampling rate from Crustal Movement Observation Network of China （CMONOC） are analyzed after the earthquake. The results show that： （1） different from previous studies, both pre-seismic amplitude perturbation and co-seismic amplitude perturbation are not critical inversely proportional to epicentral distance; （2） unlike shallow earthquake, the pre-seismic and co-seismic amplitude perturbation of gravity illustrate syn- chronous spatial variation characters with decrease of epicentral distance for Linkou earthquake. This may because Linkou earthquake is a deep earthquake and occurred in Pacific Plate subduction zone; （3） compared to basement and semi-basement, cave can provide a better observation environment for gPhone gravimeter to detect pre-seismic gravity anomalies.

Three-dimensional characteristics of focal fault of 1995 M_S=6.5 Wuding earthquake occurring in Yunnan Province

By means of the hypocenter distribution and focal mechanism of Wuding Ms=6.5 earthquake sequence occurred in1995. the space orientation and activity characteristics of focal fault of Wuding earthquake have been studied fromthe three-dimensional space-time process. The results indicate that the focal fault of Wuding earthquake is a subsurface, NWW-trending, upright and right-lateral strike slip fault which is consistent with the intensity distributionin foe meizoseisfnal region. Although the large-scale NS-trending Tanglang-Yimen active fault passes through theearthquake region. it is irrelevant to the Ms=6.5 Wuding main earthquake. Since the relationship between thestrong earthquake and the shallow geological active fault can not be determined, the crustal deep structure shouldbe studied. The method proposed in the paper can be used to distinguish the focal fault in the deep crust.

Analysis and study of the large earthquake risk in Yanqing-Huailai basin

On the basis of study results of deep sounding in the Yanqing Huailai basin, the shallow active tectonics, palaeoseismic events, seismic activity, distribution of crustal stress field and other related data are combined to study the earthquake risk of the basin comprehensively. Meanwhile, the comparison of deep structures between the basin and some other earthquake regions such as the Xingtai area is made. It is thought that there is the background of deep structures for occurrence of moderate and strong earthquakes in the Yanqing Huailai basin and its periphery, and the possibility for an M =7 earthquake to occur there cannot be excluded.

Large scale characteristic distance between strong earthquake

The global seismicity shows a characteristic distance of about 23°. The middle deep and deep earthquakes in the European and Asian blocks concentrate on several zones which separate about 23° away from earch other. The shallow strong earthquakes ( M S≥7) form belts of over 20°, the ends of these belts are near the concentration points of middle deep and deep earthuakes. The Circular Pacific island arcs, volcanoes, shallow earthquakes, middle deep and deep earthquakes also show the characteristic distance of about 23°.

Determination of the crustal structure and seismicity of the Linfen rift with S-wave velocity mapping

The Linfen rift is a Cenozoic extensional rift with significant seismicity and seismic hazards.Studies of this rift shed light on deep dynamic processes and seismogenic mechanisms relevant to crustal structure and seismic activity.We first conducted a joint inversion of receiver functions and surface wave dispersion on waveform data collected from 27 broadband seismic stations to image the crustal S-wave velocity in the Linfen rift and its surroundings.We then relocated the source parameters for 10 earthquake events with depths>20 km and studied the relationship between crustal S-wave velocity and seismicity.The results show that low-velocity zones of different scales exist in the middle-lower crust,and that the depth of the seismogenic layer gradually increases from^25 km in the south to^34 km in the north,roughly corresponding to the bottom of the low-velocity zone.We found that most of the relocated earthquakes occurred in the low-velocity zone at depths of 18 km to 34 km,with the deepest at 32 km.Two of the greatest historic earthquakes,Linfen(Ms 7.75)in 1695 and Hongtong(Ms 8.0)in 1303,occurred at the bottom of the high-velocity zone at depths of 12 km to 18 km.Our results,combined with previous studies,suggest that the upwelling mantle material below the rift did not remarkably affect the velocity structure from the bottom of the seismogenic layer down to the uppermost mantle nor heat the crust.It is likely that neither crustal-scale faults nor mantle earthquakes exist in the Linfen rift.