2015年尼泊尔M_S8.1地震的地壳重力均衡背景与地表形变响应特征

对2015年尼泊尔MS8.1地震的地壳均衡背景及其引起的地表形变特征进行了研究,结果表明:(1)尼泊尔MS8.1地震震中以南的印度板块岩石圈有效弹性厚度大约为9km,加载主要来自地幔;地震以北的拉萨地块岩石圈有效弹性厚度大约为2km,加载主要来自地表.(2)尼泊尔MS8.1地震震中以南地区的地壳均衡异常大约为-100mGal(10-5 m·s-2),但其北部的地壳均衡异常则为300~400mGal,尼泊尔MS8.1地震发生在地壳均衡负异常向正异常过渡的高梯度带上.(3)尼泊尔MS8.1地震使震中周围地区的地壳整体向南运动,最大水平位移超过1.5m,分布在震中东南.震中以北的同震垂向位移总体为负值,最大下降幅度超过0.5m,同震重力变化总体为正值,最大超过60μGal(10-8 m·s-2);震中以南的垂向位移总体为正值,最大升幅超过0.7m,同震重力变化总体为负值,最大降幅超过-120μGal.(4)尼泊尔MS8.1地震使"世界屋脊"喜马拉雅山脉产生沉降,最大同震降幅超过120mm,震后松弛效应将使"世界屋脊"持续缓慢下降.该强震使世界最高峰珠穆朗玛峰降低了2~3mm,有可能被GPS、InSAR等现代大地测量工具检测到.

Gravitational isostasy background and surface deformation response characteristics of the 2015 Nepal MS8.1 earthquake

We studied the gravitational isostasy background and the surface deformation response characteristics of the 2015 Nepal M_S8.1 earthquake. The results showed that: (1) the lithosphere effective elastic thickness of Indian block, an area south to the epicenter of 2015 Nepal M_S8.1 earthquake, is about 9 km, and the load comes mainly from the mantle. However, the lithosphere effective elastic thickness of Lhasa block, an area north to the great earthquake, is about 2 km, and the load comes mainly from the tomography. (2) The gravitational isostasy anomalies are about -100 mGal (10^-5m·s^-2) at area south to the Nepal M_S8.1 earthquake, while at area north to the earthquake, the values become 300~400 mGal. The Nepal M_S8.1 earthquake occurred at a high gradient belt where the isostasy varies from negative anomalies to positive anomalies. (3) Due to the Nepal M_S8.1 earthquake, the earth surface around the epicenter moved southward as a whole. The maximum of the co-seismic horizontal displacements is above 1.5 m, located at the area southeast to the epicenter. At the area north to the epicenter, the co-seismic vertical displacements are negative and the maximum exceeds -0.5 m, the gravity changes are positive and the maximum is above 60 μGal (10^-8m·s^-2). However, the values at the area south to the epicenter are vice versa. The maximum co-seismic vertical displacements and gravity changes are 0.7 m and -120 μGal respectively. (4) The Nepal M_S8.1 earthquake made the roof of the world, the Himalayas, decease as a whole, and the maximum decrease magnitude is more than 120 mm. It is expected the Himalayas will continue to decrease because of the relaxation effects of the mantle. The Nepal M_S8.1 earthquake made Mt. Everest decrease about 2~3 mm, which may be detectable by modern measuring tool such as GPS and InSAR.