Coseismic and post-seismic signatures of the Sumatra 2004 December and 2005 March earthquakes in GRACE satellite gravity
Coseismic and post-seismic signatures of the Sumatra 2004 December and 2005 March earthquakes in GRACE satellite gravity
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DOI：
10.1111/j.1365-246x.2007.03525.x
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发表时间：
2007-10
影响因子：
2.8
通讯作者：
I. Panet;V. Mikhailov;M. Diament;F. Pollitz;G. King;O. Viron;M. Holschneider;R. Biancale;J. Lemoine
中科院分区：
文献类型：
--
作者：
I. Panet;V. Mikhailov;M. Diament;F. Pollitz;G. King;O. Viron;M. Holschneider;R. Biancale;J. Lemoine
自2002年4月以来，GRACE卫星任务一直在测量地球重力场及其时间变化。虽然这些变化主要是由于地流体包络层内的质量传递，但它们也源于与冰川均衡调整和地震等现象相关的质量位移。然而，由于噪声和地流体信号的存在，以及GRACE的粗空间分辨率（半波长400公里），这些最后的贡献很难分离出来。在本文中，我们证明了对球体进行小波分析有助于从GRACE大地水准面产品中检索地震特征。利用GRACE大地水准面产品的小波分析，我们发现2004年12月（M w = 9.2）和2005年3月（M w = 8.7）苏门答腊地震引起的大地水准面变化可以被检测到。在GRACE分辨率下，2004年12月的地震产生了安达曼海重力场的强烈同震减弱，随后在受2004年安达曼海地震和2005年尼亚斯地震影响的区域出现松弛。我们发现了松弛的两个特征时间尺度，其中在安达曼中脊附近发生了快速变化。我们从地壳和上地幔岩石的密度变化以及安达曼海的垂直位移方面讨论了我们的同震观测。我们用地幔的粘弹性响应来解释震后信号。弛豫的瞬态分量可能表明活跃的安达曼中部盆地下方存在热的粘性物质。
S U M M A R Y The GRACE satellite mission has been measuring the Earth's gravity field and its temporal variations since 2002 April. Although these variations are mainly due to mass transfer within the geofluid envelops, they also result from mass displacements associated with phenomena including glacial isostatic adjustment and earthquakes. However, these last contributions are difficult to isolate because of the presence of noise and of geofluid signals, and because of GRACE's coarse spatial resolution (>400 km half-wavelength). In this paper, we show that a wavelet analysis on the sphere helps to retrieve earthquake signatures from GRACE geoid products. Using a wavelet analysis of GRACE geoids products, we show that the geoid variations caused by the 2004 December (M w = 9.2) and 2005 March (M w = 8.7) Sumatra earthquakes can be detected. At GRACE resolution, the 2004 December earthquake produced a strong coseismic decrease of the gravity field in the Andaman Sea, followed by relaxation in the area affected by both the Andaman 2004 and the Nias 2005 earthquakes. We find two characteristic timescales for the relaxation, with a fast variation occurring in the vicinity of the Central Andaman ridge. We discuss our coseismic observations in terms of density changes of crustal and upper-mantle rocks, and of the vertical displacements in the Andaman Sea. We interpret the post-seismic signal in terms of the viscoelastic response of the Earth's mantle. The transient component of the relaxation may indicate the presence of hot, viscous material beneath the active Central Andaman Basin.