A Discussion on Seismic Intensity——Taking the Xinjiang Area As an Example

INTRODUCTIONSeismicintensity measurestheintensityof anearthquake exerts onthe groundina certainarea .Itrepresents the averaged measurement of intensity of ground shakingin a certain scope and reflects theperception of peopleinearthquakes as well asthe areal andzonal distributions of earthquakeimpact onground buildings . The“Chinese Earthquake Intensity Scale”(Institute of Engineering Mechanics ,Chinese Academy of Sciences , 1980) describes one by one the correlative relations of huma…     

Discussion on the Relation Between the Probabilistic Distribution of Magnitude in a Seismic Province and That in an Area with Potential Seismic Source

According to the joint probabilistic distribution model of magnitude and space,the author discusses the relationship between the probabilistic distribution of magnitude in a seismic province and that in an area with potential seismic sources.The results show that if the magnitude probabilistic distribution follows the truncated exponential form in a seismic province,there must be some potential source in which the magnitude probabilistic distribution does not conform to that form.The result is consistent with the concept of "characteristic earthquake" derived from the study of actual records of seismicity and the study of geology.The author suggests that the relationship between the probabilistic distribution of magnitude in a seismic province and that in a seismic potential area must be considered in the study of the analysis of seismicity,seismic zonation and engineering seismology,for the purpose of the evaluation of the probabilistic distribution of magnitude correctly in every area with potential s     

Analysis of Seismic Risk at an Engineering Site from Site Effect Seismic Intensity Data Using the Seismotectonic Method Taking Six Reservoir Dam Sites in Western Anhui as an Example

The seismotectonic method is used to study the seismogenic structures and the maximum potential earthquake around an engineering site in order to determine the seismic risk at the site. Analysis of seismic risk from site effect seismic intensity data, in combination with regional seismo-geologieal data, using the seismotectonic method can provide a more reliable result. In this paper, taking the area of six reservoir dam sites in western Anhui as an example, we analyze the seismic risk from site effect seismic intensity data in combination with the seismotectonic conditions and find that P (I≥i) = 10% over 50 years. The result shows that the seismogenic structure and the maximum potential earthquake have a controlling effect on seismic risk from future earthquakes in the area around the site.     

A Preliminary Discussion on the Mechanism of Abnormal Intensity Zones of the M5.1 Wen＇an Earthquake in 2006

An earthquake measuring 5.1 on the Richter scale struck Wen'an county,Hebei Province on July 4,2006. No casualties have been reported,with only slight damage. The disaster level of this event is the slightest on the M4.9～5.1 events record tally since the CCDSN (China Center of Digital Seismic Network) was built in 1999. The epicenter intensity of this earthquake was low,while in areas like Beijing,which is 100km far away,abnormal high intensity zones appeared. This article discusses the reasons behind this abnormal phenomenon,with the diagrams of intensity isolines drawn by the intense seismic stations and networks in the capital circle area as references,as well as the seismogenic mechanism in the source,the seismic histories,the geological structures and the ray pathways of seismic waves in areas within 150km around the epicenter. It was concluded that the special dynamic and geological situations were the main causes for the lower intensity degree and slight damage in the epicenter area,but higher intensity in the surrounding areas.     

Research on Formation Mechanism of Asymmetric Basins, Taking the Weihe Basin as an Example

Asymmetry of the Weihe Basin is discussed in the paper,and also the master control fault,secondary control fault of asymmetric basin is proposed in the paper.The asymmetry of the Weihe Basin is expressed as follows:(1) its shape of the cross sections is asymmetrical;(2) the tectonic activity of the southern margin fault and the northern margin one is apparently different;(3) its deep tectonics is asymmetrical.Finally,we use the Weihe Basin as an example to establish a "cantilever-beam" model for calculations.The results show that:(1) flexure leads to stress accumulation and forming extensional fractures;(2) fractures slope steeply towards the free end;(3) when the length of beam becomes longer,it is possible that new extensional fractures will occur in the fixed end.     

Probabilistic Estimation of Hazard on Engineering Site Based on the Intensity of Historic Earthquakes and A Preliminary Comparison with Seismic Hazard Analysis

This paper introduces a new method to estimate the seismic hazard on engineering site.The method is mainly based on intensity data of historical earthquakes.The obvious feature of the method is to use some ideas of seismic hazard analysis and considering regional seismicity tendency.The authors depict the comprehensive method to estimate the related parameters and predict the seismic hazards for 14 sites as practical examples.Some problems are also discussed.Compared with seismic hazard analysis,this method has certain advantages,such as simpler computation,lower uncertainty and smaller sensitivity factor.Moreover total hazard P(I≥i)of a site can be examined with real historic data.The result given by the method in this paper can be more stable than that given by seismic hazard analysis nowadays.     

Study on the Relationship of Seismic Design Ground Motion at Different Fortification Levels in the Xinjiang Region

The seismic risk analysis results of 79 cities in Xinjiang are presented, and the bedrock peak ground accelerations under three seismic levels and their ratios are discussed. Then, the relationship between earthquake environments and the seismic risk analysis results of different exceeding probabilities are researched. The results show that minor and major earthquake motion parameters calculated from moderate earthquakes do not have a consistent probability and the ratio of bedrock peak accelerations under different exceedance probabilities are closely correlated with earthquake environments.     

Hierarchical Clustering Analysis of Focal Mechanism Solutions, Taking the Haicheng Earthquake Sequence as an Example

The currently used methods for analyzing a number of focal mechanism solutions are often ineffective for large samples.With the aid of the basic concept of hierarchical clustering methods for pattern recognition and in combination with the expression of focal mechanism solutions themselves,the sum of the angle between P-axes and the angle between T-axes of 2 solutions is defined as a distance,and a software for hierarchical clustering analysis by the shortest distance method and longest distance method is compiled.The number of types in the clustering results can be determined in accordance with different requirements.For focal mechanism solutions of the same type,the average position of each stress axis can be calculated by the method of vector composition and thereby the spatial orientation of the average focal mechanism solution can be determined.In order to test the feasibility and reliability of the software,hierarchical clustering analyses are made for the focal mechanism solutions of 24 earthquak     

Study on the Source Parameters of Earthquakes in the Middle Eastern Area of North Tianshan in Xinjiang

INTRODUCTIONThe study of source parameters is usually based oninversionfromobservational seismic waveformdata.Seismic wave affected bygeometric spreading,inelastic attenuation,scatteringandsite effects ofthe mediumontheir way fromsource to station.Therefo…     

The Statistical Analysis of Migration of Strong Earthquakes─Taking the North China Region as an Example

INTRODUCTIONMigrationofstrongearthquakesisaphenomenonwherebystrongearthquakestakeplaceinsuccessionincertainspatiallyregularpatterns (ZhangGuomin ,etal,2 0 0 1 ) .Seismologistsintheworldhavenoticedthisphenomenonforalongtime .Manyinstanceswerediscoveredinthepastdecades ,suchasthemigrationofstrongearthquakesalongtheNorthAnatolianFaultinTurkeysince1 939(Richter,1 958)andthemigrationofaseriesofearthquakes (MS ≥ 6 0 )aftertheMS7 9earthquakeinKwandong ,Japan (Utsu ,1 987) .Theexamplesofre…     

GPS Observation and Study on Recent Crustal Movement in the Northeastern Area of Pamir,Xinjiang

Calculation of repeated observation data at the densified GPS monitoring network in northeastern area of Pamir together with data from IGS stations in the peribphyery of the area yielded the movement rate of more than 40GPS station sites in the area,and,hence,the recent crustal deformation rate pattern and time series of fiductial GPS stations in the area were obtained.The result indicates that the principal movement direction of the GPS station sites is NNW,basically diagonal to the strike of Tianshan fold belt,i.e.a normal compression occurs in the Tianshan region.The movement pattern near Jiashi and its southwestern zone is some different from that of station sites in their surrounding areas,indicating a certain relation of tectonic deformation in Jiashi area to seismic activity during last years.The movement rate of station sites in the periphery of Taim basin less varies and its direction is basically consistent It indicates less or basically no deformation within Tarim basin.     

Local Seismic Events in the Area of Poland Based on Data from the PASSEQ 2006–2008 Experiment

PASSEQ 2006–2008 (Passive Seismic Experiment in TESZ; Wilde-Piórko et al. 2008) was the biggest passive seismic experiment carried out so far in the area of Central Europe (Poland, Germany, the Czech Republic and Lithuania). 196 seismic stations (including 49 broadband seismometers) worked simultaneously for over two years. During the experiment, multiple types of data recorders and seismometers were used, making the analysis more complex and time consuming. The dataset was unified and repaired to start the detection of local seismic events. Two different approaches for detection were applied for stations located in Poland. The first one used standard STA/LTA triggers (Carl Johnson’s STA/LTA algorithm) and grid search to classify and locate the events. The result was manually verified. The second approach used Real Time Recurrent Network (RTRN) detection (Wiszniowski et al. 2014). Both methods gave similar results, showing four previously unknown seismic events located in the Gulf of Gdańsk area, situated in the southern Baltic Sea. In this paper we discuss both detection methods with their pros and cons (accuracy, efficiency, manual work required, scalability). We also show details of all detected and previously unknown events in the discussed area.     

Research on the 3—D Seismic Structures in Qinghai—Xizang Plateau

Based on the recording data from the analogue and broadband digital seismic stations in and around Qinghai-Xizang (Tibet)Platean,the three dimensiomal 3-D) seismic velocity stroctures in Qinghai-Xizang Plateau were obtained by using the regional body wave tomography and surface wave tomography.The results from these two tomography methods have similar characteristics for P-and S-wave velocity structures in crust and upper mantle.They show that there are remarkahle low velocity zones in the upper crust of L hasa block in the southern Qinghai-Xizang Plateau and the lower crust and upper mantle of Qiangtang block in the northern Qinghai-Xizang Plateau.These phenomena may be related to the different steps of collision process in southern and northern Qinghai-Xizang Plateau.     

Seismic Inventory Simulation and Conformance Test Based on the Monte Carlo Method——A Case Study of the Fenhe-Weihe Belt

Artificial earthquake catalogue simulation is one of the ways to effectively improve the incompleteness of the existing earthquake catalogue,the scarcity of large earthquake records and the improvement of seismological research.Based on the Poisson distribution model of seismic activity and the Gutenberg-Richter magnitude-frequency relationship, the Monte Carlo method which can describe the characteristics of the stochastic nature and the physical experiment process is used.This paper simulates the future seismic catalogues of the Fenhe-Weihe seismic belt of different durations and conducts statistical tests on them. The analysis shows that the simulation catalogue meets the set seismic activity parameters and meets the Poisson distribution hypothesis,which can obtain a better simulated earthquake catalogues that meets the seismic activity characteristics.According to the simulated earthquake catalogues,future earthquake trends in this region are analyzed to provide reference for seismic hazard analysis.     

Analysis of Seismic Activity in the Middle Part of the North-South Seismic Belt—Joint Study on Deep Seismic Sounding Profile and Seismicity Parameters

Using the rich deep seismic sounding data recorded in the middle part of the North-South Seismic Belt in China, the horizontal and vertical profiles are constructed to obtain the seismic velocity structure, analyze the seismic distribution and calculate the seismic energy and the thickness of the seismogenic layer at the same time. On this basis, the seismicity parameters are calculated using the earthquake catalogue of the study area for the past 40 years, and the relationship between the b-value distribution and the velocity structure is analyzed. The results show an uneven b-value distribution in the study area and a segmented feature along the Longmenshan fault zone. Most of the earthquakes occur in the transition zone anomalies from the positive to the negative. In addition, the thickness of the crust drops from ~60 km to ~48 km from the Southeastern to the Northeastern Qinghai-Tibetan Plateau, but the thickness of the seismogenic layer increases gradually. It is speculated that the crustal composition of the Northeastern margin contains more felsic materials and has relatively stronger seismic activities than the Southeastern Qinghai-Tibetan Plateau, possibly associated with the subduction and compression of the Indian Ocean Plate.     

Primary Quantitative Study on Earthquake Damage Extracted from Remote Sensing Imagery——A Case Study of Seismic Damage in the Urban Area of Dujiangyan due to the M_S8.0 Wenchuan Earthquake

The fast developing remote sensing techniques play an increasingly important role in earthquake emergency response, disaster survey and loss estimation. As there is a lack of quantitative studies on seismic damage based on remote sensing, its practicality in seismic disaster management has usually been questioned. The paper introduces the essential quantitative study idea, the concept of the remote sensing seismic damage index (DRS_I RS) and analysis models, demonstrates the seismic damage indices (DG_IC) of buildings obtained from ground surveying and its quantitative relation to DRS_I RS in Dujiangyan city, Sichuan Province, which was destroyed by the 2008 Wenchuan earthquake with M_S8.0. The primary results show that an obvious relationship exists between the DRS_I RS of buildings obtained from the high resolution satellite or aerial remote sensing images and DG_I C or the building collapse ratio obtained through ground survey, which suggests that the quantitative study on seismic damage based on remote sensing will provide an effective method for seismic damage survey and loss estimation.     

Study of Finite Element Modeling of Strong Earthquake Activities and Its Preliminary Application—Taking Southwest China as an Example

Based on research result concerning the preparation and activity of strong earthquakes in groups and using the finite element method, a finite element dynamic model for Southwest China is established in this paper. Using this model, the stress adjustment in the whole of the Southwest China region in response to the stress change due to strong earthquake occurrence is studied. The preliminary result shows that many strong earthquakes occurred in areas where the stress heightened after the last strong earthquake. So, the finite element model set up in this paper is useful for judging the regions where strong earthquakes are likely to occur in future.     

Numerical Study on the Effect of the Manila Seismic Tsunami on the Guangdong Coast——The Nonlinear Effects of Tides and Tsunamis

The coupling numerical model between astronomical tide and tsunamis was built based on the data of the COMCOT model, which was verified by the Japan "3·11" tsunami. The tsunami source of the Manila seismic tsunami was designed and computed to analyze the risk of tsunami which will happen in the Guangdong coast. According to the results, the maximum quantity of water increasing and the time of the tsunami arriving at the Guangdong seacoast were calculated. The coupling simulation between astronomical tide and tsunamis has significant meaning for evaluating the risk and early-warning of tsunamis in the Guangdong coastal area.     

Study on Self-Affine Fractal and Multi-Fractal Features of Geomorphic System in the Tianshan Area of Xinjiang Region, China

In this paper, we use the standard deviation method and the fixed mass method to study the self-affine fractal and multi-fractal features along two topographic profiles across different tectonic-geomorphic elements in the Tianshan area of Xinjiang region, China. The results show that in the studied scaling range, the two profiles display different scaling fractal features, and the form and value range of multi-fractal spectra Dq also show different characteristics. The study suggests that the landforms are not completely random, but are deterministically random. The fractal dimension values in different scaling ranges express the mode, intensity and spatial dimension of the endogenic and exogenic processes. Meanwhile, a boundary point between the macroscopic and microscopic scales of geomorphic process is suggested to be about 5km. These results are of significance in quantitative study of geomorphic dynamics.