Capturing magma intrusion and faulting processes during continental rupture: seismicity of the Dabbahu (Afar) rift
Capturing magma intrusion and faulting processes during continental rupture: seismicity of the Dabbahu (Afar) rift
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DOI：
10.1111/j.1365-246x.2008.03877.x
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发表时间：
2008-09-01
影响因子：
2.8
通讯作者：
Buck, W. R.
中科院分区：
文献类型：
--
作者：
Ebinger, C. J.;Keir, D.;Buck, W. R.
大陆破裂模型强调断层在张性应变调节中的作用;岩墙侵入引起的张性常被忽视。2005年9月开始在埃塞俄比亚阿法尔凹陷的一个主要的裂谷事件提供了一个机会，研究应变住宿区的初期板块破裂。临时地震台阵记录的地震（2005年10月至2006年4月）、对断层模式的直接观察和大地测量数据记录了沿沿着类似于早期遥感研究中确定的60公里长的达巴胡裂谷段的持续应变和持续堤坝侵入。震中位置位于沿着一条宽约3公里、长约50公里的狭长地带，弯曲进入Dabbahu火山东南侧;第二条狭长地带继续向北朝向Gab'ho火山。考虑到9月危机中类似于8 m的开口，我们将微震活动的深度分布解释为岩墙侵入带;岩墙沿沿着类似于60 km长的构造-岩浆段从类似于10 km处上升到近地表。震源机制表明，滑动沿着NNW走向的正断层，垂直于阿拉伯-努比亚板块开口矢量。地震活动性、干涉合成孔径雷达、连续GPS和构造模式都表明，从下部或地壳下岩浆库注入的岩浆在主幕后至少持续了3个月。Dabbahu火山两个地点的持续地震群与干涉合成孔径雷达数据中确定的变形区相吻合：（1）一个椭圆形的、西北倾斜的地震活动和沉降区，被解释为岩浆通道;（2）一个更分散的、半径为8公里的浅层地震活动区（< 2公里），位于阴影区上方，被解释为地下2.5公里至6公里之间的岩浆房。干涉合成孔径雷达和连续的GPS数据显示，在区域（2）的浅源上方隆起，在大部分不活动的Gab'ho火山上方隆起。地震活动的模式提供了一个3-D的角度来看，岩浆补给系统保持沿轴分割的这一初期海底扩张段。
Continental rupture models emphasize the role of faults in extensional strain accommodation; extension by dyke intrusion is commonly overlooked. A major rifting episode that began in 2005 September in the Afar depression of Ethiopia provides an opportunity to examine strain accommodation in a zone of incipient plate rupture. Earthquakes recorded on a temporary seismic array (2005 October to 2006 April), direct observation of fault patterns and geodetic data document ongoing strain and continued dyke intrusion along the similar to 60-km long Dabbahu rift segment defined in earlier remote sensing studies. Epicentral locations lie along a similar to 3 km wide, similar to 50 km long swath that curves into the SE flank of Dabbahu volcano; a second strand continues to the north toward Gab'ho volcano. Considering the similar to 8 m of opening in the September crisis, we interpret the depth distribution of microseismicity as the dyke intrusion zone; the dykes rise from similar to 10 km to the near-surface along the similar to 60-km long length of the tectono-magmatic segment. Focal mechanisms indicate slip along NNW-striking normal faults, perpendicular to the Arabia-Nubia plate opening vector. The seismicity, InSAR, continuous GPS and structural patterns all suggest that magma injection from lower or subcrustal magma reservoirs continued at least 3 months after the main episode. Persistent earthquake swarms at two sites on Dabbahu volcano coincide with areas of deformation identified in the InSAR data: (1) an elliptical, northwestward-dipping zone of seismicity and subsidence interpreted as a magma conduit, and (2) a more diffuse, 8-km radius zone of shallow seismicity (< 2 km) above a shadow zone, interpreted as a magma chamber between 2.5 and 6 km subsurface. InSAR and continuous GPS data show uplift above a shallow source in zone (2) and uplift above the largely aseismic Gab'ho volcano. The patterns of seismicity provide a 3-D perspective of magma feeding systems maintaining the along-axis segmentation of this incipient seafloor spreading segment.