SEISMOLOGY AND GEOLOGY ›› 2014, Vol. 36 ›› Issue (3): 763-774.DOI: 10.3969/j.issn.0253-4967.2014.03.017

• CONTENTS • Previous Articles     Next Articles

DETECTION OF COSEISMIC CHANGES OF GREAT EARTHQUAKES IN GRACE TIME-VARIABLE GRAVITY FIELD WITH EMPIRICAL ORTHOGONAL FUNCTIONS:A CASE STUDY OF THE MW9.0 TOHOKU-OKI EARTHQUAKE

ZHANG Ke-liang1, GAN Wei-jun1, ZHOU Xin2,3   

  1. 1. State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China;
    2. Key Laboratory of Computational Geodynamics, Chinese Academy of Sciences, Beijing 100049, China;
    3. College of Earth Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
  • Received:2013-12-31 Revised:2014-08-08 Online:2014-09-30 Published:2014-09-30

GRACE卫星重力场同震变化的经验正交函数分解:以日本MW9.0地震为例

张克亮1, 甘卫军1, 周新2,3   

  1. 1. 中国地震局地质研究所, 地震动力学国家重点实验室, 北京 100029;
    2. 中国科学院计算地球动力学重点实验室, 北京 100049;
    3. 中国科学院大学地球科学学院, 北京 100049
  • 作者简介:张克亮|男|1981年生|2010年在中国科学院研究生院获博士学位|助理研究员|现主要从事联合GPS、GRACE数据进行构造形变监测研究|电话:010-62009661|E-mail:zkl0824@ 163.com。
  • 基金资助:

    国家自然科学基金(41174082,41172180)和中国地震局地质研究所基本科研业务专项(IGCEA1314)共同资助

Abstract:

The Tohoku-Oki MW9.0 earthquake of 11 March, 2011 has caused eastward movement and subsidence of the Japanese Islands as well as mass redistribution. The temporal-spatial features of mass redistribution were discussed by using the monthly GRACE time-variable gravity field, which would compensate the inefficiency for the undersea focal region where GPS, InSAR measurements are not available. The coseismic gravity changes were computed through least-square fitting and empirical orthogonal function(EOF) from the time series on 0.5°×0.5° grids, and through dislocation model as well. A dipole distribution of the coseismic changes appears in back-arc region and trench with maximum decrement and increment of~6μgal and~3μgal, respectively. The results suggest that EOF method avoids a priori knowledge, such as event time, as used in least squares fitting. Nevertheless, the gravity signal derived from GRACE satellites is an integral of many different geophysical processes, thus the reliability and exact physical sources are likely varying due to the event scale and observation time span, etc. In this study, most of seasonal changes are eliminated through PCs 2, 3, 4; and the coseismic gravity changes extracted from the first principle component of EOF, whose distribution is spatially coherent, are much closer to the result from dislocation model than the least square result, therefore can really reflect the changes resulting from the earthquake.

Key words: GRACE gravity field, empirical orthogonal function, least squares fitting, Tohoku-Oki MW9.0 earthquake, coseismic change, non-tectonic factors

摘要:

2011年3月11日日本东海发生MW9.0地震,造成日本岛整体东移、下沉并伴随巨大的质量重新分布。对于海底地震的震中区域,空间观测的GRACE卫星重力数据很好地弥补了GPS、InSAR等形变资料的缺失。利用GRACE卫星月重力场数据计算了地面0.5°×0.5°网格点上的重力变化时间序列,采用最小二乘拟合、经验正交函数(EOF)2种方法,提取了同震重力变化,结果显示震中两侧区域的重力变化呈两极分布,其中弧后区域重力下降,最大降幅约6μgal,海沟区域重力增加,最大增幅约3μgal。EOF方法避免了最小二乘拟合方法所需的地震发生时刻等先验信息,但卫星重力信号是由多种地球物理过程引起的重力变化的叠加,EOF结果的可靠性及其反映的真实物理来源往往随着事件的规模、观测时间的长短等而改变。文中第2,3,4主成分主要反映了非构造因素的影响,通过第1主成分空间一致性提取的同震重力变化与位错理论模型计算结果较为接近,因此较真实地反映了地震引起的重力变化特征。

关键词: GRACE卫星重力场, 经验正交函数, 最小二乘拟合, 日本MW9.0地震, 同震变化, 非构造因素

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