2011年日本MW9.0强震对天津地区地壳运动的影响分析

Effects of Japan MW9.0 Earthquake to the Crustal Movementof Tianjin Area

摘要:

处理了天津地区GNSS观测网和部分陆态网络及周边IGS站连续观测数据，分析了2011年日本MW9.0地震前后天津地区的地壳运动，并研究了此次地震对天津地区地壳运动的影响。结果显示：2011年日本MW9.0地震对天津地区的影响主要是水平方向，垂直方向影响不大；水平向同震位移中EW向明显大于NS向，位移量为8.5~10.1 mm；结合区域基线向量的差异变化可以看出该地震对天津地区起到了一定的拉张作用；地震前后测站水平向运动速度差异不明显，约在0.1~2 mm/yr之间。

Abstract:

On March 11，2011，a 9.0 magnitude earthquake occurred on the east coast of Honshu， Japan （N 38.1°，E 142.6°） and triggered a strong tsunami and serious secondary disasters including damage to a nuclear power plant. This earthquake，referred to as Japan MW9.0，was due to movement of the Pacific and adjacent plates，and also caused permanent coseismic displacement in northeast China. With the establishment of the Crustal Movement Observation Network of China （CMONOC） and China Tectonic Environment Monitoring Network（CMTEMN），we can obtain the coseismic displacement through processing and analysis of GNSS post-earthquake data.These data are useful for basic research studying seismic dynamics and characteristics，and for predicting future earthquake trends.Tianjin GNSS network has 23 GNSS stations，which belong to Tianjin Institute of Surveying and Mapping and Earthquake Administration of Tianjin Municipality.This paper examines the effect of the Japan MW9.0 earthquake on the Tianjin area.First，GNSS observation data were collected for the Tianjin area，combined with CMONOC stations and IGS stations around China，and then the crustal activity of Tianjin area after the Japan MW9.0 earthquake was calculated.The data were processed by the GAMIT software and then time series and velocity fields were obtained using QOCA software. The result was analyzed through time series，coseismic displacement，change of length of baseline and the velocity field.The results showed: that many GNSS network stations were permanently displaced a few millimeters in the east direction after the earthquake.Results indicated that the impact of the Japan MW9.0 earthquake was mainly horizontal in the Tianjin area，with no significant change in the north or vertical direction.Coseismic displacement was calculated with 3-day of time-series data from before and after the earthquake.The horizontal direction of coseismic displacement of the stations was the same，namely pointing to the direction of the epicenter；the direction of coseismic displacement in the east was about 8.5~10.1 mm.The length of baseline was also calculated with the time series，and some baselines that crossed the fault were analyzed.From the long-time trend, the entire baseline has an obvious yearly cycle.From the length of the baseline，baseline GGSL-JIXN that crosses the Cangdong fault shows some tension，while baseline WQCG-JIXN that crosses the Baodi fault shows that the baseline length increased slightly after the earthquake due to tensional stress. Results showed that the earthquake created a tensional effect on Tianjin area to some extent. The velocity field changed about 0.1~2 mm/yr in the east direction，while the velocity field in the North-South direction changed only a small amount that was within the error range.