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The Magnetic Fabric of Gouge Mimics the Coseismic Focal Mechanism of the Chi‐Chi Earthquake (1999, Mw 7.6)
Geophysical Research Letters ( IF 5.2 ) Pub Date : 2020-10-22 , DOI: 10.1029/2020gl090111
Yu‐Min Chou, Charles Aubourg, En‐Chao Yeh, Sheng‐Rong Song, Yi‐Kai Lin, Fabien Humbert, Xiaodong Jiang, Teh‐Quei Lee

We present a magnetic fabric investigation of small oriented rock fragments from gouges and wall rocks from the Chelungpu fault (Taiwan), where the Chi‐Chi earthquake occurred (Mw 7.6, 1999). Samples are obtained from surface outcrops and at a depth of ~1 km, including the 3‐mm‐thick Chi‐Chi principal slip zone. Wall rocks at depth show magnetic foliation roughly parallel to bedding, whereas they are oblique at the surface. Within the gouges, the mean shape of magnetic ellipsoid is oblate, and the degree of anisotropy is up to 12%. The magnetic foliation diverges of ~40° from the fault plane, compatible with a simple shear westward. The magnetic lineation is oblique, resulting probably from coseismic and interseismic records. The reconstructed focal mechanism from the magnetic fabric closely matches the focal mechanism solutions for the Chi‐Chi earthquake. Our work demonstrates that magnetic fabric of gouge fragments can bring valuable kinematic information on modern earthquakes.

中文翻译:

凿子的磁性结构模仿了Chi-Chi地震的同震震源机制(1999,Mw 7.6)

我们提供了一种磁结构调查方法,该方法是对发生自Chi-Chi地震(M w7.6,1999)。从地表露头获得样品,深度约1 km,包括3 mm厚的Chi-Chi主滑带。深处的围岩显示出与层理大致平行的磁裂,而在地表则倾斜。在圆孔内,椭球体的平均形状为扁圆形,各向异性程度高达12%。磁层裂距断层平面约40°,与简单的向西切变兼容。磁线倾斜,可能是由于同震和间震记录造成的。从磁性织物重建的震源机制与Chi-Chi地震的震源机制解非常匹配。我们的工作表明,凿碎碎片的磁性结构可以为现代地震带来有价值的运动学信息。
更新日期:2020-11-15
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