2016年熊本Mw7.1地震前GPS形变特征分析

摘要

利用日本九州岛地区连续GPS观测数据,分析了2016年熊本Mw7.1地震前的区域地壳变形演化特征.GPS速度场和应变率场显示,熊本地震前右旋剪切应变积累区主要集中在断层上盘的九州中部块体(CKY)内,断层下盘的南海弧前块体(NFY)和九州南部块体(SKY)表现为显著的绕块体中心的逆时针刚性旋转运动;熊本地震发生在右旋剪切应变率高值区的边缘,且发震断层附近区域GPS应变时序结果显示自2014年后右旋剪切应变呈逐渐增强趋势;平行断层方向的GPS速度剖面结果显示发震断层上盘右旋剪切应变积累特征显著,表现为越靠近断层处的滑动速率越小,且断层西北侧站点速率随离开断层距离的增加呈非线性趋势变化.另外,GPS剖面结果显示,日奈久断层近场存在1 ～2 mm/a的相对滑动,可能存在浅层蠕滑运动.%We studied the characteristics of crustal deformation and variations of deformation in short terms before the 2016 Kumamoto Mw7.1 earthquake by using continuous GPS in Kyushu Island.The GPS velocity and strain rate field between Oct.2012 and Mar.2016 showed dextral shear movements between two sides of the causative fault and most strain accumulated by the west side block named CKY block.Otherwise,the velocity field in blocks NFY and SKY which are located in the east side of the causative fault showed typical counterclockwise rotation.The epicenter of the Kumamoto earthquake locates at the edge of the highest dextral shear strain area,and time-series of the first shear strain showed dextral strain was gradually increased from 2014.What's more,the GPS profiles across the Hinagu fault showed significant dextral shear strain accumulation with 1 ～ 2 mm/a relative slip rate in near-field,which may indicated creep movement of the Hinagu faults in upper crust area.