A Characteristic Analysis of the Dynamic Evolution of Preseismic-Coseismic-Postseismic Interferometric Deformation Fields Associated with the M 7.9 Earthquake of Mani,Tibet in 1997

By using the D-InSAR technique, we have acquired the temporal-spatial evolution images of preseismic.cosesimci-postseismic interferometric deformation fields associated with the M 7.9 earthquake of Mani, Tibet on 8 November 1997. The analysis of these images reveals the relationships between the temporal-spatial evolution features of the interferometric deformation fields and locking, rupturing, and elastic restoring of the source rupture plane, which represent the processes of strain accumulation, strain release, and postseismic restoration. The result shows that 10 months prior to the Mani event, a left-lateral shear trend appeared in the seismic area, which was in accordance with the earthquake fault in nature. The quantity of local deformation on the north wall was slightly larger than that on the south wall, and the deformation distribution area of the north wall was relatively large. With the event impending, the deformation of the south wall varied increasingly, and the deformation center shifted eastward. Two and half monthd before the event, the west side of the fault was still locked while the east side began to slide, implying that the whole fault would rupture at any moment. These features can be regarded as short-term precursors to this earthquake. Within the period from 16 April 1996 to two and half months before the earthquake, the most remarkable deformation zones appeared in the north and south walls, which were parallel to and about 40 km apart from the fault, with accumulated local displacements of 344 mm and 251 mm on the north and south walls, respectively. The south wall was the active one with larger displacements. Five months after the earthquake, the distribution feature of interferometric fringes was just opposite to that prior to the event, expressing evident right-lateral shear. The recovered displacements are -179 mm on the north wall and -79 mm on the south wall, close to the east side of the fault. However, in the area of the south wall far from the fault there still existed a trend of sinistral motion. The deformation of the north wall was small but recovered fast in a larger area, while the active south wall began to recover from the east section of the fault toward the WSW.

3-D finite element modeling for evolution of stress field and interaction among strong earthquakes in Sichuan-Yunnan region

Based on the latest achievement about activities of geological structure, a 3-D finite-element model containing four layers of upper crust, lower crust (two layers) and upper mantle is established in the paper. By repeated tests and revisions, the boundary conditions of the model are determined. And then the background stress field, the stress field caused by fault creep and the stress field triggered by strong earthquake in Sichuan-Yunnan region, as well as their dynamic variations are calculated. The results indicate that the latter earthquake often occurs in the area with positive Coulomb rupture stress change associated with the former one, the former earthquake has a triggering effect on the latter one to a certain extent, and strong earthquake often occur in groups under the background of high stress, which is of great significance for distinguishing seismic anomalies, as well as for improving the level of earthquake prediction.

Anomalies of geophysical field in deep crustand earthquakes in Central-South Shanxi

Comprehensive studies on the crustal structures, the anomalies of geophysical field and the seismicity in Central-South Shanxi are conducted. The research results show that there are deep tectonic background for occurring moderate earthquakes in Lingshi-Jiexiu region between Linfen and Taiyuan. From now on, the region should be attached closely.

The idea and project of the “Medium－Scale Experiment Field for Earthquake Prediction”──Research on observations and applications of mining earthquake in Mentougou Coal Mine

A brief account of the development of the research on mining earthquakes and the general situation of the Mentougou Coal Mine medium scale experiment field for earthquake prediction and the project of monitor and prediction is given. The differences of waveforms between mining earthquakes and natural earthquakes is discussed. The magnitude frequency distribution of the 79 000 mining earthquakes of over M L1.0 from 1984 to 1995 is summarized . Finally, taking PH and PV, the principal compressive stress components of the focal mechanism of the mining earthquakes, as the criteria, analyses the stress background of the 12 large mining earthquakes.

Main Factors Affecting the Distribution of the Macroscopic Destruction Field of Earthquake

It is proposed that some possible macroseismic epicenters can be determined quickly from the relationship that the microseismic epicenters located by instruments bear with faults. Based on these so-called macroseismic epicenters, we can make fast seismic hazard estimation after a shock by use of the empirical distribution model of seismic intensity. In comparison with the method that uses the microseismic epicenters directly, this approach can increase the precision of fast seismic hazard estimation. Statistical analysis of 133 main earthquakes in China was made. The result shows that the deviation distance between the microseismic epicenter and macroseismic epicenter falls within the range of 35 km for 88 % earthquakes of the total and within the range of 35 to 75 km for the remaining ones. Then, we can take the area that has the microseismic epicenter as its center and is 35 km in radius as the area for emphatic analysis, and take the area within 75 km around the microseismic epicenter as the area for general analysis. The relation between the 66 earthquake cases on the N-S Seismic Belt in China and the spatial distribution characteristics of faults and the results of focal mechanism solution were analyzed in detail. We know from the analysis that the error of instrumental epicenter determination is not the only factor that gives effects to the deviation of the macroseismic epicenter. In addition to it, the fault size, fault distribution, fault activity, fault intersection types, earthquake magnitude, etc. are also main affecting factors. By sorting out, processing and analyzing these affecting factors, the principle and procedures for quickly determining the possible position of the macroseismic epicenter were set up. Taking these as a basis and establishing a nationwide database of faults that contains relevant factors, it is possible to apply this method in practical fast estimation of seismic hazard.

Coseismic displacement estimate of the 2013 M_S7.0 Lushan, China earthquake based on the simulation of near-fault displacement field

Usually, GPS observation provides direct evidence to estimate coseismic displacement. However, GPS stations are scattered, sparse and cannot provide a detailed distribution of coseismic displacement. Strong ground motion records share the same disadvantages as GPS in estimating coseismic displacement. Estimations from InSAR data can provide displacement distributions; however, the resolution of such methods is limited by the analysis techniques. The paper focuses on estimating the coseismic displacement of the Ms7.0 Lushan earthquake on April 20, 2013 using a simulation of the wave field based on the elastic wave equation instead of a quasi-static equation. First, the media and source models were con- structed by comparing the simulated velocity and the record velocity of the ground motion. Then simulated static displacements were compared with GPS records. Their agreement validates our results. Careful analysis of the distribution of simulated coseismic displacements near the fault reveals more details of the ground motion. For example, an uplift appears on the hanging wall of the fault, rotation is associated with the horizontal displacement, the fault strike and earthquake epicenter provide the main control on motion near the faults, and the motion on the hanging wall is stronger than that on the footwall. These results reveal additional characteristics of the ground motion of the Lushan earthquake.

Statistical analysis on energy field of seismicity in Ningxia and its neighborhood region

The random function theory is used in the paper. Taking the regional seismicity energy as the random function of space and time, the features of small seismicity field in Ningxia and its neighborhood region are studied by the analytical method of natural orthogonal function expansion. The chief part of the field, i.e., the temporal changes of time weight coefficients of first several typical fields is analyzed. We have found that their values had upward and downward changes of a large amplitude before moderate-strong earthquakes and showed variation features correlating to moderate-strong earthquakes occurred in the region and its surrounding areas. From the earthquake examples in Ningxia region, we can make the conclusion that the method of natural orthogonal function expansion of earthquake energy stochastic field is an earthquake analysis and prediction method that is worth further exploration.

Fault plane parameters of Sanhe-Pinggu M8 earthquake in 1679 determined using present-day small earthquakes

The great Sanhe-Pinggu M8 earthquake occurred in 1679 was the largest surface rupture event recorded in history in the northern part of North China plain. This study determines the fault geometry of this earthquake by inverting seismological data of present-day moderate-small earthquakes in the focal area. We relocated those earthquakes with the double-difference method. Based on the assumption that clustered small earthquakes often occur in the vicinity of fault plane of large earthquake, and referring to the morphology of the long axis of the isoseismal line obtained by the predecessors, we selected a strip-shaped zone from the relocated earthquake catalog in the period from 1980 to 2009 to invert fault plane parameters of this earthquake. The inversion results are as follows： the strike is 38.23°, the dip angle is 82.54°, the slip angle is -156.08°, the fault length is about 80 km, the lower-boundary depth is about 23 km and the buried depth of upper boundary is about 3 kin. This shows that the seismogenic fault is a NNE-trending normal dip-slip fault, southeast wall downward and northwest wall uplift, with the right-lateral strike-slip component. Moreover, the surface rupture zone, intensity distribution of the earth-quake and seismic-wave velocity profile in the focal area all verified our study result.

Moment tensor inversion for focal mechanism of the Beibuwan earthquakes

Two earthquakes of Ms=6.0 and Ms=6. 1 consecutively occurred on December 31, 1994 and January 10, 1995 in Beibuwan region, China. By using the generalized reflection-transmission coefficient matrix and the discrete slowness integration method in the calculation of Green's functions, we obtained the focal mechanisms of these earthquakes using long-period waveforms of regional body waves recorded by the China Digital Seismograph Network (CDSN) by means of moment tensor inversion method in frequency domain. The results inverted indicate that the focal mechanisms of these two earthquakes were similar to each other. Their principal compressional stresses are in NW-SE direction and principal tensional stresses are in NE-SW direction. It turns out that the occurrence of the two earthquakes was controlled by the same tectonic environment related to the collision of the Philippine Plate and the Eurasian Plates. On the other hand, the results imply that the stress field in the seismogenic region has a significant change after the Ms=6.0 earthquake. It may be proposed that the occurrence of the Ms=6. 1 earthquake could be related to the stress field adjustment caused by the Ms=6.0 earthquake.

Preseismic deformation associated with the 2014 Ms7.3 Yutian earthquake derived from GPS data

Based on analysis of the GPS data during 1999-2007,2009-2011,and 2011-2013 mainly from the Crustal Motion Observation Network of China,we obtained the GPS horizontal velocity field,the GPS strain rate field,and the profiles across the southwestern segment of the Altyn Tagh Fault zone and its adjacent regions and identified the different characteristics of horizontal crustal deformation fields and profiles during different periods. The results show that,before the February 12,2014,Ms7. 3 Yutian earthquake,the laevorotation deformation along the southwestern segment of the Altyn Tagh Fault zone increased about 3. 3 mm /a during 2011-2013,relative to that in 2009-2011,and the GPS strain rate field distributed in the southeastern segment of the Altyn Tagh Fault during 2011-2013 increased obviously. These abnormal changes may be regarded as precursors to the Ms7. 3 Yutian earthquake.

Study on Precursory Features of the Lop M_S6. 0 Earthquake Based on GPS Continuous Observation Data and Mobile Gravity Data

Through calculating and analyzing of GPS continuous observation data and mobile gravity data,the study results from the data are as follows.( 1) The different movement rate of the fault ends provides conditions for stress accumulation.( 2) The high value zone of gravity anomaly appeared in the monitoring area before the earthquake,and gravity variation contour lines are parallel to the strike of fault; and the process of enhancingweakening-enhancing appeared in the regional gravity field before earthquake.

Contemporary kinematic models and moment deficit of Chinese mainland

There are lots of achievements about kinematics of Chinese mainland and its vicinity determined from historic earthquake data, Quaternary fault rates and geodesy observations, which provide basic data for analysis of seismic hazard in study areas. Based on impreciseness in using energy of 47 earthquakes with magnitude greater than 7.0 in previous study, we firstly collected source parameters, surface ruptures and displacements of major earthquakes carefully, and divided them into small segmentations with these data gathered. Secondly, we determined contemporary deformation field from latest earthquake mechanisms, Quaternary fault slip rates and geodesy observations. Finally, we evaluated moment deficit of study areas from historic earthquake data and predicted deformation field, and removed 10 percent of aseismic deformation. Combining with previous results, we analyzed the seismic hazard of study areas. The results show that there are some areas with large moment deficit in Chinese mainland. There are also large moment deficit areas, including regions around the Ordos Block, southeastern coast of China and the Bakal rift zone. Previous studies show that there may be some potential earthquakes in the near future in Darts of areas mentioned above.