Comparative Study of Global Seismicity on the Hot Engine Belt and the Cooling Seismic Belt—Improvement on Research Ideas of Earthquake Prediction

The study in this paper analyzes and compares the distribution on the global engine active seismic zone and cooling seismic belt basing on the ANSS earthquake catalog from Northern California Earthquake Data Center. An idea of the seismogenesis and earthquake prediction research is achieved by showing the stratigraphic structure in the hot engine belt. The results show that the main engine and its seismic cones are the global seismic activity area, as well as the subject of global geological disaster. Based on the conjecture of other stratum structure, the energy of crustal strong earthquake and volcano activities probably originates from the deep upper mantle. It is suggested that the research on earthquake and volcano prediction should focus on the monitor and analysis on the sub-crustal earthquake activities.

Seismicity anomalies before the great earthquake of M_S=8.1 in the Kunlun Pass and its significance to earthquake prediction

A great earthquake of MS=8.1 took place in the west of Kunlun Pass on November 14, 2001. The epicenter is lo-cated at 36.2N and 90.9E. The analysis shows that some main precursory seismic patterns appear before the great earthquake, e.g., seismic gap, seismic band, increased activity, seismicity quiet and swarm activity. The evolution of the seismic patterns before the earthquake of MS=8.1 exhibits a course very similar to that found for earthquake cases with MS7. The difference is that anomalous seismicity before the earthquake of MS=8.1 involves in the lar-ger area coverage and higher seismic magnitude. This provides an evidence for recognizing precursor and fore-casting of very large earthquake. Finally, we review the rough prediction of the great earthquake and discuss some problems related to the prediction of great earthquakes.

Seismicity Quantification and Its Application to Medium-term Earthquake Prediction

Bed on the analysis of each parameter describing seismicity,we think A(b)-value can betterquantitatively describe the feature of the enhancement and quietness of seismicity in this paper. Thedata of moderate or small earthquakes during 1972～1996 in North China are used in space scanningof A(b)-value. The result shows that 2～3 years before most strong earthquakes there wereObviously anomaly zones of A(b)-value with very good prediction effect. Some problems about themedium-term prediction by using A(b)-value are also discussed.

Seismic characteristics near the epicenter of the 1303 Hongtong M=8 earthquake, Shanxi Province and its implication

In this paper, we calculated the seismic pattern of instrumental recorded small and moderate earthquakes near the epicenter of the 1303 Hongtong M=8 earthquake, Shanxi Province. According to the spatial distribution of small and moderate earthquakes, 6 seismic dense zones are delineated. Temporal distribution of ML2 earthquakes since 1970 in each seismic dense zone has been analyzed. Based on temporal distribution characteristics and historical earthquake activity, three types of seismicities are proposed. The relationship between seismic types and crustal medium is analyzed. The mechanism of three types is discussed. Finity of strong earthquake recurrence is pro-posed. Seismic hazard in mid-long term and diversity of earthquake disaster in Shanxi seismic belt are discussed.

The 2018 M_S 5.9 Mojiang Earthquake:Source model and intensity based on near-field seismic recordings

On September 8, 2018, an M_S 5.9 earthquake struck Mojiang, a county in Yunnan Province, China. We collect near-field seismic recordings(epicentral distances less than 200 km) to relocate the mainshock and the aftershocks within the first 60 hours to determine the focal mechanism solutions of the mainshock and some of the aftershocks and to invert for the finite-fault model of the mainshock.The focal mechanism solution of the mainshock and the relocation results of the aftershocks constrain the mainshock on a nearly vertical fault plane striking northeast and dipping to the southeast. The inversion of the finite-fault model reveals only a single slip asperity on the fault plane. The major slip is distributed above the initiation point, ～14 km wide along the down-dip direction and ～14 km long along the strike direction, with a maximal slip of ～22 cm at a depth of ～6 km. The focal mechanism solutions of the aftershocks show that most of the aftershocks are of the strike-slip type, a number of them are of the normal-slip type, and only a few of them are of the thrust-slip type.On average, strike-slip is dominant on the fault plane of the mainshock, as the focal mechanism solution of the mainshock suggests, but when examined in detail, slight thrust-slip appears on the southwest of the fault plane while an obvious part of normal-slip appears on the northeast, which is consistent with what the focal mechanism solutions of the aftershocks display. The multiple types of aftershock focal mechanism solutions and the slip details of the mainshock both suggest a complex tectonic setting, stress setting, or both. The intensity contours predicted exhibit a longer axis trending from northeast to southwest and a maximal intensity of Ⅷ around the epicenter and in the northwest.

Relation between the evolution of seismic apparent strain field and the region of strong earthquake occurrence

In this paper, according to the data on the middle and strong earthquakes in China, we have preliminary studied the relation between the characteristic of space-time evolution of the seismic apparent strain field and the regions of 31 macroseism events since 1955. The result shows that, there is a rather well correlation between the anomaly region of seismic apparent strain and the zone of macroseism event occurrence within the time range of one to about five years. The R value of the application of the abnormal region of seismic apparent strain to predicting the area of strong earthquake occurrence is 0.458, and the empirical possibility of forecasting the region of macroseism occurrence is 0.625, and so the forecasting effect is comparatively well. Finally, the main results obtained above are discussed preliminarily.

Seismic characteristics near the epicenter of the 1303 Hongtong M=8 earthquake, Shanxi Province and its implication

In this paper, we calculated the seismic pattern of instrumental recorded small and moderate earthquakes near the epicenter of the 1303 Hongtong M=8 earthquake, Shanxi Province. According to the spatial distribution of small and moderate earthquakes, 6 seismic dense zones are delineated. Temporal distribution of ML2 earthquakes since 1970 in each seismic dense zone has been analyzed. Based on temporal distribution characteristics and historical earthquake activity, three types of seismicities are proposed. The relationship between seismic types and crustal medium is analyzed. The mechanism of three types is discussed. Finity of strong earthquake recurrence is pro-posed. Seismic hazard in mid-long term and diversity of earthquake disaster in Shanxi seismic belt are discussed.

Seismic hazard prediction using multispectral amplification maps in a complex topographic area: A case study of Qiaozhuang town, Sichuan Province, Southwest China

Earthquakes can cause widely distributed slope failures and damage in mountainous areas.The accurate prediction of ground motions in mountainous areas is essential for managing the seismic risk of urban cities near mountains but is restricted primarily by complex seismic site amplification effects in areas of uneven terrain.This study selected Qiaozhuang town located in the Qingchuan–Pingwu fault zone,Southwest China,as a case study.A simulator for mapped seismic responses using a hybrid model(Si Se RHMap)was applied to compute the multispectral seismic topographic amplification maps at the three slope units surrounding Qiaozhuang town(Weigan hill,Mt.Dong,and Mt.Shizi).Post-earthquake damage survey maps,1 D seismic site response spectral ratios,and H/V spectral ratios of earthquake data were used to validate the computed seismic site amplification factors and resonance frequencies.The results suggest that strong topographic amplification effects usually occur at distinct slope locations,such as hilltops,convex slope positions,upslope,and narrow ridges.The computed topographic amplification factors in the study area reached up to 2.4 at upslope or hilltops,and the resonance frequencies were between 3 and 10 Hz.Topographic effects can be as important as stratigraphic effects when assessing seismic amplification effects in the study area.We conclude that both topographic and stratigraphic effects should be considered in the comprehensive seismic hazard assessment of the study area or other similar mountain towns.

Pre-seismic and Co-seismic Crustal Movements of the M 7.3 Kyushu Earthquake on April 16,2016 in Japan

The time series of coordinates of a large number of GPS stations in the world,processed by Prof. Geoffrey Blewitt with GIPSY software are available at http://geodesy. unr. edu.Based on the time series of coordinates in the global reference frame of IGS08 at more than250 stations of continuous GPS observations,downloaded from the website,the co-seismic displacements of the M7. 3 Kyushu earthquake on April 16,2016 in Japan and the preseismic strain accumulations and displacements in the regional reference frame were obtained. The station of continuous GPS observation at BJFS near Beijing has been quite stable in displacement in the eastern part of China for more than 17 years since the beginning of its operation,and this station is used as the core station in the regional reference frame for the pre-seismic displacement of the Kyushu earthquake of M7. 3. The main feature of the pre-seismic displacements of the Kyushu earthquake is characterized by locking in the crust at and near the epicenter. The anomalous pre-seismic strain accumulation developed in an area of anomalous accumulation of the shear strain component of γ1 on the northeast side of the epicenter,with increasing size of the area and increasing magnitude in γ1. The largest area covered by the anomalous γ1 is about 2000 km2. The change in the E component at BJFS since November 26,2015 was caused by the replacement of the receiver and the antenna at the station. In order to study the shortterm change in displacements at stations at and near the epicenter,the time series at 3 stations with continuous GPS observations,2 at SUWN and DAEJ in south Korea and 1 at BJSH near Beijing were analyzed. The analysis shows that the displacements at the 3 stations have been quite stable in the same manner in east Asia. Thus,BJSH is used as the core station in the regional reference frame of displacement and the displacement time series show that there were no significant short term anomalies before the earthquake.

Double Earthquakes Classification and Seismic Precursors

In this paper, we examine both the sequence and organisation of major shallow earthquakes occurred in various areas of the world from 1904 to 2017. We aim to describe their major features and how they are connected with foreshocks and aftershocks immediately close in time and space. Examining magnitude value’s fluctuations over time, we see that they form a basic pattern, consisting of three maxima, one of which is central, and two or more events preceding and following it, whose magnitude, in some cases, may be comparable. The retrospective analysis of earthquakes’ patterns of high comparable magnitude has allowed their classification along with the development of some statistically significant relationships between epicentral distance and magnitude difference and between time interval and delay among maxima as well as the identification of activation signals predicting their occurrence. The pattern we identified in seismic sequences analysis, in relation to minor shocks-generated activation signals’ positions may be used to obtain useful information for the evolutionary study of seismic sequences and for predicting double and multiple earthquakes. The graphic analysis procedure applied to the pattern enables us to know the period of seismic sequence’s greatest hazard after a strong earthquake.

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.

Study of the Seismicity of Strong Earthquakes in the Yunnan Area

Yunnan is located in the east margin of the collision zone between the India Plate and the Eurasian Plate on the Chinese Continent, where crustal movement is violent and moderatestrong earthquakes are frequent. In addition, the area features marked active block movement. Therefore, Yunnan is a perfect place for research on strong earthquake activity. Through the study on the temporal and spatial distribution of the M ≥ 6.7 earthquakes and the related earthquake dynamics in Yunnan in the last century, we conclude that the four seismically active periods, which are characterized by alternative activity in the east and the west part of Yunnan, possibly result from a combination of active and quiescent periods in each of the east and west part. And for every 100 years, there may be a period in which strong earthquakes occur in the east and west parts simultaneously. In addition, the seismicity of strong earthquakes in Yunnan corresponds well to that in the peripheral region. The seismicity of the great earthquakes in the Andaman-Myanmar Tectonic Arc belt indicates, to some extent, the beginning of a seismically active period in Yunnan. The seismicity of strong earthquakes in east Yunnan is closely related to that in Sichuan. Strong earthquakes in Sichuan often occur later than those in Yunnan. Furthermore, in the east part of Ynnnan, the three procedures including continuous occurrence of moderate-strong earthquake, quiescent period, and the occurrence of the first strong earthquake may be the style of the beginning of the earthquake active period. The above cognition is helpful to the study of earthquake prediction, seismogenic mechanism, and the dynamics of the plate margin in Yunnan.

The NE Directed Seismicity Belt in Tibet after the M_S8.1 Nepal Earthquake and Its Predictive Significance

After the 2015 M_S8. 1 Nepal earthquake,a strong and moderate seismicity belt has formed in Tibet gradually spreading along the northeast direction. In this paper,we attempt to summarize the features and investigate the primary mechanism of this behavior of seismic activity,using a 2-D finite element numerical model with tectonic dynamic settings and GPS horizontal displacements as the constraints. In addition,compared with the NEtrending seismicity belt triggered by the 1996 Xiatongmoin earthquake,we discuss the future earthquake hazard in and around Tibet. Our results show that: the NE-directed seismicity belt is the response of enhanced loading on the anisotropic Qinghai-Tibetan plateau from the Indian plate and earthquake thrusting. Also,this possibly implies that a forthcoming strong earthquake may fill in the gaps in the NE-directed seismicity belt or enhance the seismic hazard in the eastern( the north-south seismic zone) and western( Tianshan tectonic region) parts near the NE-directed belt.

Relationship between crustal magnetic anomalies and strong earthquake activity in the south segment of the China North-South Seismic Belt

The south segment of the China North-South Seismic Belt is located in the southeast margin of the Qinghai Tibet Plateau.This region is characterized by the frequent seismic activity in Chinese mainland.In this paper,the geomagnetic field model NGDC-720 and the data of terrestrial heat flow are used to investigate the distribution of crustal magnetic anomalies,the depth of Curie surface,and the characteristics of the crustal thermal structure in the south segment of the North-South Seismic Belt.The distribution characteristics of the vertical component AZ and the magnetic declination AD in the area with earthquakes over a magnitude of 6 and their aftershocks since 1970 are focused on.The results show that the earthquakes are mainly observed in the area of negative magnetic anomaly or the strong and weak transition zone.It especially shows in the AD.The Curie surface in the study area varies significantly,ranging from 20.8 to 31 km.The uplift area of the Curie surface is consistent with the high-value area of terrestrial heat flow.The high geothermal area corresponds to the strong earthquake activity area.The focal depth of most strong earthquakes is shallower than the depth of the Curie surface.The strong earthquakes mainly occur in the deep-shallow transition zones of the Curie surface.The results can be used as a reference for strong earthquake prediction in this area.

New Seismic Zoning Map of Chin a and Its Application in Earthquake Disaster Mitigation

The New Seismic Zoning Map of China was prepared from 1987 to 1990 and officially promulgated in 1991.In comparison with the previous two seismic zoning maps prepared in 1957 and 1977,some new methods were applied to upgrade the method currently used for seismic hazard analysis.First,a probabilistic method was used instead of the deterministic analysis was used for previous mapping.Second,by taking advantages of the long history of historical seismic data in China,the nonhomogeneity of seismicity both in space and in time has been fully considered and hence the over-and/or underestimation of seismic hazard could be avoided.Third,the results of middle-and long-term earthquake prediction based on tectonic evidence have been incorporated into seismic hazard analysis.In addition,the attenuation laws for both intensity and peak acceleration of strong motion as the mapping parameters are also presented.Finally,an evaluation of the New Seismic Map and its effect on engineering application,such as aseismic

Seismic Sequence Characteristics of the March 21,2008,M_S 7. 4 Yutian,Xinjiang Earthquake and Seismological Anomalies before the Earthquake

The parameters, stress field background, geological tectonics and seismic sequence of the March 21, 2008, Ms7.4 Yutian, Xinjiang earthquake are discussed in this paper. The characteristics of seismic activity in the epicenter and its adjacent region before the earthquake are analyzed; and a comparison is made between the Ms7.4 Yutian earthquake sequence, the Wenchuan Ms8.0 earthquake sequence and the Wuqia Ms6.9 earthquake sequence. The results show the Ms7.4 Yutian earthquake occurred in the junction between the Aityn Tagh fault and the western Kunlun fault, resulting perhaps from the tensile fracture of the branch fault located southwest of the Ashikule basin due to left-lateral dislocation of the Aityn Tagh fault; the seismic sequence is of main shock-aftershock type, the strongest aftershock being Ms5.8. The aftershocks attenuated quickly, and occurred in groups; the focal mechanism solutions and epicenter distribution have revealed a unilateral rupture source of this earthquake. Seismic activity shows that there was medium and medium-short term abnormity before the earthquake, but there was not short-imminent abnormity. Seismic activity of this earthquake sequence enhanced before the Ms8. 0 Wenchuan and the Ms6. 9 Wuqia earthquakes, showing the window effect to some extent.

Late-Quaternary Slip Rate and Seismic Activity of the Xianshuihe Fault Zone in Southwest China

The Xianshuihe fault zone is a seismo-genetic fault zone of left-lateral slip in Southwest China. Since 1725, a total of 59 Ms ≥ 5.0 earthquakes have occurred along this fault zone, including 18 Ms 6.0–6.9 and eight Ms ≥ 7.0 earthquakes. The seismic risk of the Xianshuihe fault zone is a large and realistic threat to the western Sichuan economic corridor. Based on previous studies, we carried out field geological survey and remote sensing interpretation in the fault zone. In addition, geophysical surveys, trenching and age-dating were conducted in the key parts to better understand the geometry, spatial distribution and activity of the fault zone. We infer to divide the fault zone into two parts： the northwest part and the southeast part, with total eight segments. Their Late Quaternary slip rates vary in a range of 11.5 mm/a –（3±1） mm/a. The seismic activities of the Xianshuihe fault zone are frequent and strong, periodical, and reoccurred. Combining the spatial and temporal distribution of the historical earthquakes, the seismic hazard of the Xianshuihe fault zone has been predicted by using the relationship between magnitude and frequency of earthquakes caused by different fault segments. The prediction results show that the segment between Daofu and Qianning has a possibility of Ms ≥ 7.0 earthquakes, while the segment between Shimian and Luding is likely to have earthquakes of about Ms 7.0. It is suggested to establish a GPS or In SAR-based real-time monitoring network of surface displacement to cover the Xianshuihe fault zone, and an early warning system of earthquakes and post seismic geohazards to cover the major residential areas.

Seismic pattern treatment method through calculation of seismic density at grid nodes

Analysis of seismic data and seismicity characteristics in China, we gave a method to deal with seismic patterns by calculating density at grid nodes. Number of earthquakes and epicenter distribution are considered comprehensively in this method. Effect of datum accuracy is stressed on parameter confirmation. Seismic patterns from this method are stable and can reflect seismic characteristics reliably. These seismic patterns are the base of quantitative analysis of seismicity. It can be applied in seismic tendency analysis and medium-long term earthquake prediction, earthquake countermeasure and risk mitigation.

V_p/V_s Anisotropy and Implications for Crustal Composition Identification and Earthquake Prediction

The ratio of P- to S-wave velocities （Vp/Vs） is regarded as one of the most diagnostic properties of natural rocks. It has been used as a discriminant of composition for the continental crust and provides valuable constraints on its formation and evolution processes. Furthermore, the spatial and temporal changes in Vp/Vs before and after earthquakes are probably the most promising avenue to understanding the source mechanics and possibly predicting earthquakes. Here we calibrate the variations in Vp/Vs in dry, anisotropic crustal rocks and provide a set of basic information for the interpretation of future seismic data from the Wenchuan earthquake Fault zone Scientific Drilling （WFSD） project and other surveys. Vp/Vs is a constant （Ф0） for an isotropic rock. However, most of crustal rocks are anisotropic due to lattice-preferred orientations of anisotropic minerals （e.g., mica, amphibole, plagioclase and pyroxene） and cracks as well as thin compositional layering. The Vp/Vs ratio of an anisotropic rock measured along a selected pair of propagation-vibration directions is an apparent value （Фy） that is significantly different from the value for its isotropic counterpart （Ф0）. The usefulness of apparent Vp/Vs ratios as a diagnostic of crustal composition depends largely on rock seismic anisotropy. A 5% of P- and S-wave velocity anisotropy is sufficient to make it impossible to determine the crustal composition using the conventional criteria （Vp/Vs≤1.756 for felsic rocks, 1.756〈Vp/Vs≤1.809 for intermediate rocks, 1.809〈Vp/Vs≤1.944 for mafic rocks, and Vp/V2〉1.944 fluidfilled porous/fractured or partially molten rocks） if the information about the wave propagation-polarization directions with respect to the tectonic framework is unknown. However, the variations in Vp/Vs measured from borehole seismic experiments can be readily interpreted according to the orientations of the ray path and the polarization of the shear waves with respect to the present-day principal stress directions （i.e., the orientation of cracks） and the frozen fabric （i.e., foliation and lineation）.

Earthquake prediction from China's mobile gravity data

The relation between plate tectonics and earthquake evolution is analyzed systematically on the basis of 1998-2010 absolute and relative gravity data from the Crustal Movement Observation Network of China. Most earthquakes originated in the plate boundary or within the fault zone. Tectonic deformation was most intense and exhibited discontinuity within the tectonically active fault zone because of the differential movement; the stress accumulation produced an abrupt gravity change, which was further enhanced by the earthquake. The gravity data from China's Mainland since 2000 obviously reflected five major earthquakes （Ms 〉 7）, all of which were better reflected than before 2000. Regional gravity anomalies and a gravity gradient change were observed in the area around the epicenter about 2 or 3 years before the earthquake occurred, suggesting that gravity change may be a seismic precursor. Furthermore, in this study, the medium-term predictions of the Ms7.3 Yutian, Ms8.0 Wenchuan, and Ms7.0 Lushan earthquakes are analytically pre- sented and evaluated, especially to estimate location of earthquake.