Yu Zhiteng, Singh Satish C, Gregory Emma P M, Maia Marcia, Wang Zhikai, Brunelli Daniele
Université de Paris, Institut de Physique du Globe de Paris, CNRS, Paris, France.
CNRS-Université de Bretagne Occidentale, IUEM, France.
Sci Adv. 2021 Apr 9;7(15). doi: 10.1126/sciadv.abf3388. Print 2021 Apr.
Oceanic transform faults, a key element of plate tectonics, represent the first-order discontinuities along mid-ocean ridges, host large earthquakes, and induce extreme thermal gradients in lithosphere. However, the thermal structure along transform faults and its effects on earthquake generation are poorly understood. Here we report the presence of a 10- to 15-kilometer-thick in-depth band of microseismicity in 10 to 34 kilometer depth range associated with a high-temperature (700° to 900°C) mantle below the brittle lithosphere along the Romanche mega transform fault in the equatorial Atlantic Ocean. The occurrence of the shallow 2016 moment magnitude 7.1 supershear rupture earthquake and these deep microearthquakes indicate that although large earthquakes occur in the upper brittle lithosphere, a substantial amount of deformation is accommodated in the semibrittle mylonitic mantle that resides at depths below the 600°C isotherm. We also observe a rapid westward deepening of this band of seismicity indicating a strong lateral heterogeneity.
大洋转换断层是板块构造的关键要素，代表着大洋中脊沿线的一级间断面，发生大地震，并在岩石圈中引发极端热梯度。然而，人们对转换断层沿线的热结构及其对地震发生的影响了解甚少。在此，我们报告，在赤道大西洋罗曼什巨型转换断层沿线，脆性岩石圈下方10至34公里深度范围内，存在一个10至15公里厚的微震深度带，该深度带与高温（700°至900°C）地幔相关。2016年发生的浅源矩震级7.1级超剪切破裂地震以及这些深源微地震的出现表明，尽管大地震发生在上部脆性岩石圈，但大量变形发生在等温线600°C以下深度的半脆性糜棱岩化地幔中。我们还观察到这条地震带迅速向西加深，这表明存在强烈的横向非均质性。
