龙门山断裂带南段岩石圈磁场变化分析

根据巴颜喀拉块体东部2011—2014年3期岩石圈磁场年变化情况,结合地壳应力资料,重点分析龙门山断裂带南段的岩石圈磁场变化与应力积累的关系。该区域2011—2012年和2012—2013年岩石圈磁场变化明显弱于周边区域,实测地壳应力结果反映汶川M_S8.0地震震后应力积累水平很高。压磁效应分析认为汶川M_S8.0地震后该区域高应力积累、低应变率的动力学背景是控制该区域岩石圈磁场弱变化的主要因素。此外,芦山M_S7.0地震及康定M_S6.3地震前震中区存在局部岩石圈磁场水平矢量的弱变化现象,尤其是2012—2013年水平矢量大小和方向均与周边区域相比存在明显差异,这可能是两次地震的前兆异常。

Variation of the Lithospheric Magnetic Field in the Southern Segment of the Longmenshan Fault Zone

According to known annual variations in the lithospheric magnetic field along the eastern segment of the Bayan Har block during the 2011-2014 period and crust stress data, the relationship between the lithospheric magnetic field and stress accumulation in the southern segment of the Longmenshan fault zone was studied. Annual variations in the lithospheric field in the local area was weaker than for surrounding areas during 2011-2012 and 2012-2013. High-stress accumulation was reflected in in-situ crust stress measurement after the Wenchuan M_S8.0 earthquake. Based on analysis of the piezomagnetic effect, it was concluded that the tectonic background of high-stress accumulation and low strain rate in the local area after Wenchuan M_S8.0 earthquake was the main factor controlling the weak variations in the lithospheric magnetic field. Additionally, the horizontal component of the lithospheric field in the area of the epicenter became weak before the Lushan M_S7.0 and Kangding M_S6.3 earthquakes. Both magnitude and direction of the horizontal vector for the 2012-2013 period differed across the surrounding area, which may be a precursor of two earthquakes.