WAS THERE SIGNIFICANT VERTICAL CRUSTAL MOTION IN EPICENTRAL REGION PRIOR TO 2008 GREAT WENCHUAN EARTHQUAKE？

doi:10.3969/j.issn.0253-4967.2014.04.002

Abstract

Abstract:

The May 12, 2008 M_S 8.0 Wenchuan earthquake has been the greatest catastrophic event occurring in China since the 1976 Tangshan earthquake. Following the earthquake, GPS data observed in the epicentral region were analyzed, and one study, based on analysis of independent 30s interval's instantaneous positions, claimed that significant vertical crustal displacement occurred one hour prior to the earthquake. This result has raised community expectations to achieve short-term and imminent earthquake prediction using the technique of high-rate GPS monitoring. High-rate GPS is an important technique developed in recent years, and has been widely used for studying short term crustal deformation during an earthquake and earthquake rupture process. Its precision and reliability of data analysis result, however, is constrained by a variety of factors, in particular, the cycle-slip detection and the integer ambiguity resolution of carrier phase are strongly dependent on the distance between the observation site and reference site (for double-differencing analysis) or satellite ephemeris and clock errors (for non-differencing analysis). We propose a new method to analyze dynamic displacements of GPS sites based on carrier phase residuals obtained from static GPS data processing. Assuming that an observation station moves during a time period in which the data are processed, the carrier phase residuals of static data post-processing are mainly reflecting the position displacements and multipath effect. Taking advantage of periodic repeatability of the multipath effect in a sidereal day, we develop a model to reduce/remove the multipath component in the carrier phase residuals, and extract the observation station dynamic displacement signals relative to the station mean position. We apply this method to derive the dynamic displacement time series of 3 continuous GPS stations (CHDU, PIXI, and DUJY) located in the epicentral region of the Wenchuan earthquake. Our result shows that vertical displacements of the 3 sites within 7 days prior to the earthquake are within 2cm, and the disturbances appear to be random than progressive. The resolved dynamic displacements in two consecutive days are also shown to be highly correlated, suggesting that there was no significant disturbance caused by external error source or deformation source. This conclusion is true also for the day (and even one hour) prior to the earthquake. Combining with the analysis of the coseismic deformation pattern, we conclude that there was no significant crustal motion in the epicentral region prior to the Wenchuan earthquake.

Key words: GPS, static/dynamic data processing, Wenchuan earthquake, vertical crustal deformation

摘要：

2008年5月12日的汶川M_S 8.0地震是自1976年唐山地震以来发生在中国大陆的最大灾难事件.地震发生后有人通过对GPS数据的动态处理分析认为在地震前1小时内震中附近有非常显著的地壳垂直运动发生, 从而提升了地震学界对通过高频GPS观测技术实现地震短临预报的预期.高频GPS观测技术是近年来GPS技术发展的一个重要方面, 在研究地震前后地壳形变短期变化过程、地震震源破裂过程等方面取得了非常广泛的应用, 但数据解算的精度和可靠性还是受到多种因素的制约.文中提出了一种基于数据静态处理得到的载波相位观测残差来分析测站位置动态变化的方法, 并采用这种方法对汶川地震前震中附近几个GPS连续站的数据进行分析, 结果表明汶川地震前震中附近并不存在显著的地壳运动.

关键词: GPS, 静态/动态数据处理, 汶川地震, 地壳垂向形变

CLC Number:

P315.72⁺5

WANG Min, SHEN Zheng-kang. WAS THERE SIGNIFICANT VERTICAL CRUSTAL MOTION IN EPICENTRAL REGION PRIOR TO 2008 GREAT WENCHUAN EARTHQUAKE？[J]. SEISMOLOGY AND GEOLOGY, 2014, 36(4): 956-963.

王敏, 沈正康. 2008年汶川大地震临震前震中附近是否存在显著的地壳垂直运动？[J]. 地震地质, 2014, 36(4): 956-963.

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