汶川地震近震源区地形变短期前兆现象的解析

2008年汶川8.0级地震是我国自建国以来灾难最为严重的一次强地震,有关震前该区域地壳变形情况引起许多学者的关注。本文给出了沿龙门山地震带地倾斜及跨龙门山断裂断层水准剖面临震前变化的特征:汶川地震前沿龙门山地震带分布的康定、汶川及茂县台地倾斜无明短期显变化;6个断层水准观测场地,除耿达场地观测到较大幅度变化有争议外,其他断层观测场震前均未观测到突出的短临前兆性异常变化。本文分析了汶川地震前大区域地震活动性资料及震前沿南北地震带显著形变异常点分布特点,探讨了汶川地震震中区域应变积累过程,认为近震源区域无显著短期前兆变化现象很可能与震中区域介质所具有的高应变、小变形性质有关。另外,也不排除地形变观测点所处的位置等有关因素。

On the Short-term Precursory Phenomena of Ground Deformation Associated with the 2008 Ms8.0 Wenchuan Earthquake

The 12 May 2008 MS8.0 Wenchuan earthquake is one of the most catastrophic event in the past 60 years in China.Great attention has been paid by a lot of scholars.In this paper,we studied the pre-seismic deformation characteristics of ground tilt along the earthquake rupture zone and leveling across the rupture zone.We showed that before the eartthquake some tiltmeters installed along the Longmenshan seismic belt were in operation and no significant changes have been observed at Kangding,Wenchuan and Maoxian stations,and there were also no reliable precursors among 6 cross-fault levelling observation sites,except the large changes observed at the Gengda site which has been denied as a precursor anomaly by mathematical modelling.We analyzed the regional seismic activity data and significant deformation anomalie on South-northern seismic belt,and studied the strain accumulation process of Wenchuan earthquake.We proposed that no significant short-term precursory changes around the epicentral area was possibly related to the properties of high-strain but small deformation state prior to the main shock,but the factors of deformation measurement sites and the kinds of measurement instruments could not be excluded.