Study on the Moment Magnitude of Small and Moderate Earthquakes Located in the Inner Mongolia Region

Based on digital seismic waveform data from Inner Mongolia Digital Seismic Network,the source spectrum parameters of 182 small and moderate earthquakes from January,2009to September,2016 are derived,and the seismic momentmoment magnitude MW of the earthquakes are calculated.Theand the relationship between stress drop and magnitude are obtained using the linear regression method.It is clear that incorporating the moment magnitude into the seismic quick report catalog and the official earthquake catalog can enrich earthquake observation report content,thus providing better service for earthquake emergency and earthquake scientific research.

Research on the Seismic Wave Characteristics of Low Frequency Signals before the Alxa Left Banner MS5.8 Earthquake in Inner Mongolia,China

In order to search for the seismic wave characteristics of low frequency signals in the Alxa Left Banner region,Inner Mongolia,the low frequency signals of seismic wave data are extracted from the earthquakes of MS5. 8 in 2015 and MS5. 0 in 2016 in this area. The results show that:① Before the MS5. 8 earthquake,the seismic stations located near the epicenter in Wuhai,Dongshengmiao,and Shizuishan recorded seismic waves that showed the phenomenon of spectrum shift from high to low frequency.② The low frequency signals recorded by different stations have obvious difference.③ According to the data recorded by the station closest to the epicenter,low-frequency signals were recorded about120 hours before the earthquake and had obvious anomalies. This may reflect slow slip before the earthquake.

The Focal Depth Analysis of the Inner Mongolia-Ningxia Border Area Earthquakes

We selected the 103 M_L≥2. 5 earthquake waveform data from the Inner Mongolia-Ningxia border during 2009-2015,which was recorded by the Inner Mongolia Digital Seismic Networks and used the simplex method, Hyposat method, double difference location method,and deterministic method (PTD) for the determination of focal depth,and compared the results. The CAP moment tensor inversion method is used to determine the focal depths of the Alxa Left Banner M5. 8 and M4. 2 earthquakes. The final results of the focal depth by the deterministic method (PTD) and the double difference location method fit well with the tectonic characteristics of the Inner Mongolia-Ningxia border area,but those of the simplex method and the Hyposat method do not. The average depth of the Inner Mongolia-Ningxia border seismic tectonic zone is 13. 32 ± 8 km.

Determination of Focal Depths of the MS5.8 Alxa Left Banner,Inner Mongolia Earthquake Sequence

Using the double-difference earthquake location algorithm,the deterministic method (PTD method) and the CAP seismic moment tensor inversion method,the paper selects the primary waveform data of 78 earthquakes recorded by the "China Earthquake Science Array Probe Project in the Northern Part of North South Seismic Belt ",the "China Earthquake Scientific Exploration Array Data Center"of Institute of Geophysics,China Earthquake Administration,and the Inner Mongolia Digital Seismic Network to calculate the focal depths of the mainshock and the seismic sequence of the M_S5.8 Alxa Left Banner earthquake in Inner Mongolia. The results show that the focal depth of the main shock is 20. 6 km,determined by the double-difference earthquake location method,18. 1 km by the PTD method,and 19. 2 km by the CAP method. The focal depth of the earthquake sequence calculated by the double-difference location method is larger. The deterministic method (PTD method) and double-difference location method are the methods that fit the tectonic characteristics of the seismic source area,and the CAP method is suitable for larger earthquakes.

The Conversion Relationship between the Local Earthquake Magnitude and Surface Wave Magnitude in the Inner Mongolia Digital Seismic Network

Using 116 earthquakes over M_L3.8 in the Inner Mongolia region from 2008 to 2015, the local earthquake magnitude M_L and surface wave magnitude M_S are remeasured. Based on norm linear regression(SR1 and SR2) and norm(OR) orthogonal regression method, we established the conversion relationship between M_L and M_S. The results were tested with Gaussian disturbance. The result shows that the orthogonal regression method(OR) result has the best fitting curve, and the conversion relation is M_S=0.96 M_L-0.10. The difference between our result and Guo Lücan's(M_S=1.13 M_L-1.08) may be caused by regional tectonic characteristics. M_(S Inner Mongolia) value is significantly higher than the M_(S empirical) value, with an average difference of 0.23, the difference distribution of empirical relation and the rectified relation is in the range of 0.2-0.3.

The Crustal Velocity Structure of Western Inner Mongolia

The terrain of Inner Mongolia is long and narrow, and the geological structure is complicated. The South China crustal velocity model and Inner Mongolias optimal crustal velocity model 2015 cannot fully meet the earthquake location requirements of Inner Mongolia. Based on the seismological observations produced by Inner Mongolia Seismic Digital Network from 2009 to 2016,the initial model was obtained by using the linear fit of the seismic phases and the converted travel time curve. The Hyposat results of 225 earthquakes that occurred in western Inner Mongolia were scanned using this model,and the velocity model for western Inner Mongolia was determined as follows: V1= 6. 06 km/s;VPb= 6. 61 km/s; Vn= 8. 12 km/s; H1= 30 m; and the Moho depth H = 44 km. Comparison of the test results of the new model and the reference model shows that the residual error of the new model and the mean deviation of the epicenter location have obviously decreased.

Spatial Correlation Anomalies of the Diurnal Variation of the Geomagnetic Vertical Component before the Yingjiang MS 6.1 and Ludian MS 6.5 Earthquakes

Significant anomalies were observed at the geomagnetic stations in the southwest region of China before the Yingjiang M_S6. 1 earthquake and the Ludian M_S6. 5 earthquake in 2014.We processed the geomagnetic vertical component diurnal variation data by the spatial correlation method. The results show that during the period from April 1 to May 20,2014,there existed quasi-synchronous decrease changes in the coefficient curves between the five geomagnetic stations of Guiyang,Hechi,Nanshan,Muli,Yongning and Xinyi and Hongshan stations. Furthermore,there was a high gradient zone in the normalized correlation coefficient contour map with background values removed. The epicenters of the Yingjiang M_S6. 1 earthquake and the Ludian M_S6. 5 earthquake are located in the gradient zone or near the gradient zone.

Focal Mechanism and Focal Depth of the May 22,2016 M S 4.6 Earthquake in Chaoyang,Liaoning

An earthquake with M_S4. 6 occurred at 17: 08 p. m.,May 22,2016 in Chaoyang County,Liaoning Province. We used the P-wave first motion method,TDMT method,and CAP method to determine the focal mechanisms and the PTD method and sP n-Pn method to determine the focal depth. The focal mechanism results of the three methods are consistent. The depth results of the CAP method,PTD method and sP n-Pn method are close. We used the double difference location method to relocate earthquakes in 2009-2016,and obtained the strikes and dip angles of the small earthquake distributions with the help of simulated annealing algorithm and gauss Newton algorithm fitting. According to the focal mechanism results,the depth results,the characteristics of small earthquake distributions and the structural characteristics of the source area,the seismogenic fault strike is NEE and the main pressure force direction is NNW. The earthquake focal mechanism is for a normal fault type with a little left-lateral strike slip motion.

Focal mechanism and seismogenic structure of the Shiqu MS4.4 earthquake

The focal mechanism solution of the Shiqu MS 4.4 earthquake occurred on May 16th,2017 in Sichuan Province is studied by the gCAP method using the waveform data from the regional seismic networks in Sichuan,Qinghai,Tibet and Gansu provinces.The strike/dip/dipping angle of the first nodal plane are 214/80/167and those of the second nodal plane are 306/77/10,the optimal centroid depth is 7.30.6 km and the moment magnitude is MW 4.5.Furthermore,the study investigates the robustness of the results against the error of crustal velocity structure,location,data quality and difference of seismic parameters,subsequently obtaining a stable resolved focal mechanism.According to the geological structure in the seismogenic area,spatial distribution of aftershock sequenceof the regional tectonic stress field,and the focal mechanism of the main shock,we suggest that the Shiqu earthquake is induced by a left-lateral strike-slip mechanism and the second nodal plane is inferred to be the seismogenic fault,consistent with the geometry of the Changshagongma fault which is the secondary fault of the northwest part of the Xianshuihe fault zone.

Application of the Levenberg-Marquardt Method in Improving Technology of the Seismic Influence Field

Attenuation relation of seismic intensity is fitted by using 152 complete isoseismic lines from65 earthquakes which were greater than MS4. 0 from 1940 to 2015 in Inner Mongolia and neighboring regions. Meanwhile,based on the difference of land form and geological structure characteristics,the study area is the divided into eastern,western and central.The intensity attenuation relationships are established separately by using the LM( Levenberg-Marquardt) method and elliptic attenuation model. Comparisons are made by using the earthquake affecting field model of North China and computed results. The analytical study shows that the relation obtained represents the features of earthquake damage distribution in the areas well,and has positive meaning to guide loss assessments immediately after a destroyed earthquake.

The Tongliao MS5.3 Earthquake and Its Foreshock Determination

Taking the 2013 Tongliao MS5. 3 earthquake as a research subject, on the basis of statistical analysis of earthquake sequence using the HypoDD location method and focal mechanism solutions,the paper analyzes and discusses the relationship between the ML4. 4 and MS5. 3 earthquakes. The results show that the Tongliao MS5. 3 earthquake occurred under the background of medium-small earthquakes long-term quiescence and short-term enhancement in the epicentral area. The results of accurate seismic location shows that the Tongliao MS5. 3 earthquake sequence is distributed in the NW direction,extending 10 km,and the ML≥3. 0 aftershocks are concentrated south of the mainshock. The distance between the MS5. 3 mainshock and the ML4. 4 foreshock is about 1. 8 km,with a focal depth of 7. 208 km and 7. 089 km,respectively,their focal location is very close,and may have occurred on the same fault plane. The results of focal mechanism shows that the Tongliao MS5. 3 earthquake is of the strike-slip type,the focal mechanism of aftershocks are disordered,and with time lapse,the type is changed from strike-slip to thrust and normal faulting. The bigger foreshocks had similar focal mechanism and were all normal fault types,which exhibits to some extent,an obvious crustal medium anisotropy in the epicentral area before macroscopic rupturing,as represented by alignment fractures,with stress action enhanced,this"consistency"of seismic precursor regime would gestate the mainshock. According to the characteristics of temporal-spatial distribution of earthquake sequence and similarity of focal mechanism,we judge that the Tongliao MS5. 3 earthquake sequence is a foreshock-mainshock-aftershock type.

Study on the Anisotropy of the Underground Medium in Hohhot

In this paper,the data of earthquake events of magnitude MS6.0 and above produced in Hohhot Seismic Station from 2008 to 2015 and the data of0 seismic events from2015 to 2016 in Horinger Seismic Station and the surrounding mobile stations in southern Hohhot are selected.Using Splitlab and SAM software,the spin-correlation method,the least-energy method and the cross-correlation coefficient method are used to analyze the teleseismic and near-seismic phases(SKS,S).The results of this study are in good agreement with the results previously obtained by other researchers.The study of teleseismic SKS splitting reflects the characteristics of the anisotropy of the upper mantle beneath Hohhot,that is,the anisotropy of the upper mantle shows NW,which reflects"fossil"Anisotropy,mainly in the continental structure of stable units and preserves the history of mantle deformation information.The crustal anisotropy reflected by the nearearthquake S-wave splitting study is similar to that of the active fault zone,trending NE as a whole and is consistent with the tectonic stress field background of the northeastern margin of Ordos block.