Intense interface seismicity triggered by a shallow slow slip event in the Central Ecuador subduction zone
Intense interface seismicity triggered by a shallow slow slip event in the Central Ecuador subduction zone
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厄瓜多尔中部俯冲带浅层慢滑事件引发强烈界面地震活动
DOI：
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发表时间：
2013
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影响因子：
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通讯作者：
M. Chlieh
中科院分区：
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作者：
M. Vallée;J. Nocquet;J. Battaglia;Y. Font;M. Segovia;M. Régnier;P. Mothes;P. Jarrín;D. Cisneros;Sandro Vaca;H. Yepes;X. Martin;N. Béthoux;M. Chlieh
我们记录了2010年8月发生在拉普拉塔岛（厄瓜多尔）下方，1906年Mw = 8.8大逆冲断层地震破裂区以南的一个长达1周的慢滑事件（SSE），等效矩震级为6.0-6.3。GPS数据显示，SSE发生在约10 km的深度，在浅（<15 km）的下倾部分，隔离，锁定补丁沿着俯冲界面。位于拉普拉塔岛（SSE上方10 km）的宽带地震仪和连续大地测量站的可用性，使得能够仔细分析沿着俯冲界面缓慢和快速应力释放过程之间的关系。在慢滑动序列期间，地震资料显示当地地震活动急剧增加，共检测到650多个地震，其中50个地震的矩震级在1.8 - 4.1之间。然而，通过地震释放的累积力矩最多只占由GPS位移估计的总力矩释放的0.2%。大多数最大的地震位于沿着或非常接近俯冲界面，震源机制与板块相对运动一致。虽然地震规模呈现经典分布（古滕贝格-里希特定律，B-值接近1），但时空发生呈现特定模式。首先，最大的地震似乎是随机发生在慢滑动序列，这进一步证明了地震活动是由应力波动驱动的与非滑动滑动。此外，在SSE期间观察到的地震活动包括个别事件和重复地震的家庭。这些观测结果表明，由幕式地震滑动引起的应力增量既可能导致地震矩的突然释放，也可能导致小的闭锁块体内的渐进破裂。这项研究提供了一个地震成因的后验解释中厄瓜多尔俯冲带，强烈的地震群已定期观察（1977年，1998年，2002年和2005年）。这些群可能是由大规模的缓慢滑动事件触发的。
We document a 1 week long slow slip event (SSE) with an equivalent moment magnitude of 6.0–6.3 which occurred in August 2010 below La Plata Island (Ecuador), south of the rupture area of the 1906 Mw = 8.8 megathrust earthquake. GPS data reveal that the SSE occurred at a depth of about 10 km, within the downdip part of a shallow (<15 km), isolated, locked patch along the subduction interface. The availability of both broadband seismometer and continuous geodetic station located at the La Plata Island, 10 km above the SSE, enables a careful analysis of the relationships between slow and rapid processes of stress release along the subduction interface. During the slow slip sequence, the seismic data show a sharp increase of the local seismicity, with more than 650 earthquakes detected, among which 50 have a moment magnitude between 1.8 and 4.1. However, the cumulative moment released through earthquakes accounts, at most, for 0.2% of the total moment release estimated from GPS displacements. Most of the largest earthquakes are located along or very close to the subduction interface with focal mechanism consistent with the relative plate motion. While the earthquake sizes show a classical distribution (Gutenberg‐Richter law with a b‐value close to 1), the space‐time occurrence presents a specific pattern. First, the largest earthquakes appear to occur randomly during the slow slip sequence, which further evidence that the seismicity is driven by the stress fluctuations related to aseismic slip. Moreover, the seismicity observed during the SSE consists in individual events and families of repeating earthquakes. These observations indicate that the stress increment induced by the episodic aseismic slip may lead both to sudden seismic moment release and to progressive rupture within small locked patches. This study offers an a posteriori interpretation of the seismogenesis in the Central Ecuador subduction zone, where intense seismic swarms have been regularly observed (1977, 1998, 2002, and 2005). These swarms have likely been triggered by large‐magnitude slow slip events.