Vannucchi Paola, Clarke Alexander, de Montserrat Albert, Ougier-Simonin Audrey, Aldega Luca, Morgan Jason P
Università degli Studi di Firenze, Firenze, 50121, Italy.
University College London, Gower Street, London, WC1E 6BT, UK.
Nat Commun. 2022 Apr 28;13(1):2311. doi: 10.1038/s41467-022-29944-8.
Non-volcanic tremor is a particularly enigmatic form of seismic activity. In its most studied subduction zone setting, tremor typically occurs within the plate interface at or near the shallow and deep edges of the interseismically locked zone. Detailed seismic observations have shown that tremor is composed of repeating small low-frequency earthquakes, often accompanied by very-low-frequency earthquakes, all involving shear failure and slip. However, low-frequency earthquakes and very-low-frequency earthquakes within each cluster show nearly constant source durations for all observed magnitudes, which implies characteristic tremor sub-event sources of near-constant size. Here we integrate geological observations and geomechanical lab measurements on heterogeneous rock assemblages representative of the shallow tremor region offshore the Middle America Trench with numerical simulations to demonstrate that these tremor events are consistent with the seismic failure of relatively weaker blocks within a stronger matrix. In these subducting rocks, hydrothermalism has led to a strength-inversion from a weak matrix with relatively stronger blocks to a stronger matrix with embedded relatively weaker blocks. Tremor naturally occurs as the now-weaker blocks fail seismically while their surrounding matrix has not yet reached a state of general seismic failure.
非火山性震颤是一种特别神秘的地震活动形式。在其研究最多的俯冲带环境中，震颤通常发生在板块界面内，位于震间锁定带浅部和深部边缘处或附近。详细的地震观测表明，震颤由重复出现的小低频地震组成，常常伴有甚低频地震，所有这些地震都涉及剪切破裂和滑动。然而，每个地震群内的低频地震和甚低频地震对于所有观测到的震级而言，其震源持续时间几乎恒定，这意味着震颤子事件震源具有近乎恒定的大小特征。在此，我们将对中美洲海沟近海浅部震颤区域具有代表性的非均质岩石组合进行的地质观测和地质力学实验室测量与数值模拟相结合，以证明这些震颤事件与较强基质中相对较弱岩块的地震破裂相一致。在这些俯冲岩石中，热液活动导致了强度反转，从具有相对较强岩块的弱基质转变为嵌入相对较弱岩块的强基质。当现在较弱的岩块发生地震破裂而其周围基质尚未达到普遍地震破裂状态时，震颤就自然发生了。
