Tao Xia-xin

Relationships between moment magnitude and fault parameters: theoretical and semi-empirical relationships

Fault parameters are important in earthquake hazard analysis. In this paper, theoretical relationships between moment magnitude and fault parameters including subsurface rupture length, downdip rupture width, rupture area, and average slip over the fault surface are deduced based on seismological theory. These theoretical relationships are further simplified by applying similarity conditions and an unique form is established. Then, combining the simplified theoretical relationships between moment magnitude and fault parameters with seismic source data selected in this study, a practical semi-empirical relationship is established. The seismic source data selected is also to used to derive empirical relationships between moment magnitude and fault parameters by the ordinary least square regression method. Comparisons between semi-empirical relationships and empirical relationships show that the former depict distribution trends of data better than the latter. It is also observed that downdip rupture widths of strike slip faults are saturated when moment magnitude is more than 7.0, but downdip rupture widths of dip slip faults are not saturated in the moment magnitude ranges of this study.

WebGIS Based Information and Decision-Making Support System for Earthquake Disaster Reduction

The development of Earthquake Disaster Reduction System (EDRS) depends on the state of arts of computer technology, involving many fields of computer application skills and techniques. In this paper, first a key period after earth quake occurrence is discussed. Then a Web GIS based Information and Decision-making Support System (the System) for Earth quake Disaster Reduction is introduced, including of technical frame works, function composition, structure of software, redevelopment languages, data bases, and remote linking and calling of analysis modules. Mean while tested by a Ms5.1 earth quake in north-east China, the System showed the damage distribution maps, which include the comparison of isoseismals map and the damage of buildings map. Finally, several conclusions are presented.

Prediction of near-field strong ground motions for scenario earthquakes on active fault

A method to predict near-field strong ground motions for scenario earthquakes on active faults is proposed. First, macro-source parameters characterizing the entire source area, i.e., global source parameters, including fault length, fault width, rupture area, average slip on the fault plane, etc., are estimated by seismogeology survey, seismicity and seismic scaling laws. Second, slip distributions characterizing heterogeneity or roughness on the fault plane, i.e., local source parameters, are reproduced/evaluated by the hybrid slip model. Finally, the finite fault source model, developed from both the global and local source parameters, is combined with the stochastically synthetic technique of ground motion using the dynamic corner frequency based on seismology. The proposed method is applied to simulate the acceleration time histories on three base-rock stations during the 1994 Northridge earthquake. Comparisons between the predicted and recorded acceleration time histories show that the method is feasible and practicable.

Internet information aided disaster assessment of great earthquake

The information on Internet is distributing in a large space scope and can be almost updated in real time at a short time period; especially, as “information highway”, Internet is a cheap information source, it costs less workload and time to collect information from Internet, and it can play a helpful role in disaster mitigation. The 5.12 Wenchuan earthquake is taken as a case study in this paper to develop a set of methods to aid the disaster assessment of the great earthquake from internet information. Firstly, the information of the damaged area was collected successively after the shock that were released on Internet website of the authoritative organization with data mining technology. The information was then analyzed, arranged and classified into three types, the information on damage distribution, the statistic data on death and injures, and those on building collapse rate in residential areas assessed by the remote sensing data. This information was further translated into “information based intensity”, and the locations of those residential areas with “information based intensity” were searched out from the fundamental geographic information database, and were stored into database together. The isoseismals were constructed by GIS spatial modeling tools from the experiential intensity attenuation relationships. A Human-computer interactive method was developed to improve the isoseismals successively by the data of information based intensity. The results at several time periods were compared with the ground survey which published a couple of months later, and showed that the isoseismals were improved step by step closely to the survey with the information amount increasing. On the 12th day after the earthquake, the improved isoseismals was already quite similar with the survey. The result can roughly show the actual damage situation, and provide quickly a support to the disaster relief.

An Idea to Simulate the Environmental Vibration Caused by Urban Rail Traffic

In most studies, the vibration source is modeled as random vibration with a given power spectral density at the nearest point from the rail, and the effect on buildings and human beings is further calculated by a two dimensional calculation. However, from 3 dimensional point of view, it is far away from the fact that the effect is come from many points along the rail while the trains move through rapidly. Two-step is defined to simulate environmental vibration. In the first step, the train-track system is simplified as a series of subsystems. Taking into account the track power irregularity, each subgrade reaction under ballast block was calculated when trains move on the track. All the forces constitute point source array to simulate the source. In the second step, the foundation is simulated as isotropic layered media, combined with artificial boundary conditions in the calculation border region, using the decoupling finite element method to calculate the surface environmental vibration. The simulation result was compared with those from field observation in Beijing, China. The result is quite close to the field observation data, and provides a good foundation for further study on environmental vibration impact to buildings and human beings.

Observation and Prediction of Strong Ground Motion in China

Development and current status of the strong ground motion measurement and interpretation in China are described.