CEA, DAM, DIF, 91297, Arpajon, France.
Aix Marseille Univ, CNRS, IRD, Coll. France, CEREGE, Aix-en-Provence, France.
Sci Rep. 2023 Mar 20;13(1):4566. doi: 10.1038/s41598-023-30697-7.
Large earthquakes breaking the frontal faults of the Himalayan thrust system produce surface ruptures, quickly altered due to the monsoon conditions. Therefore, the location and existence of the Mw8.3 1934 Bihar-Nepal surface ruptures remain vividly disputed. Even though, previous studies revealed remnants of this surface rupture at the western end of the devastated zone, ruptures extent remains undocumented in its central part. Evidence for recent earthquakes is revealed along the frontal thrust in this region. The Khutti Khola river cuts an 8 m-high fault scarp exposing Siwalik siltstone thrusted over recent alluvial deposits, with faults sealed by a colluvial wedge and undeformed alluvial sediments. Detrital charcoals radiocarbon dating reveals that the last event occurred between the seventeenth century and the post-bomb era, advocating for the 1934 earthquake as the most recent event. In the hanging wall, fluvial terraces associated with fault scarps were abandoned after a penultimate event that happened after the tenth century, a rupture we associate with the historic earthquake of 1255CE. Slips of 11-17 m and 14-22 m for the 1934 and 1255 earthquakes, respectively, compare well with the ~ 10-15 m slip deficit accumulated between the two earthquakes, suggesting that most of the deformation along the front is accommodated by surface-rupturing earthquakes.
大型地震沿着喜马拉雅逆冲系统的前缘断裂带产生地表破裂，但由于季风的影响，这些破裂很快就会发生改变。因此，1934 年发生在比哈尔邦和尼泊尔的Mw8.3 级地震的地表破裂的确切位置和存在情况仍存在争议。尽管之前的研究在受灾最严重区域的西部边缘发现了该次地表破裂的残余部分，但在其中心部分，破裂的延伸情况仍未记录在案。该地区沿前缘逆冲带揭示了近期地震的证据。Khutti Khola 河切割出一道 8 米高的断层陡崖，暴露了被新近冲积物覆盖的西瓦立克粉砂岩，断层被堆积楔和未变形的冲积沉积物所封闭。碎屑木炭放射性碳测年表明，最近的一次事件发生在 17 世纪到原子弹爆炸后的时代之间，这表明 1934 年地震是最近的一次地震。在前缘逆冲带，与断层陡崖相关的河流阶地在末次事件后被废弃，末次事件发生在 10 世纪之后，我们将这次破裂与 1255 年的历史地震联系起来。1934 年和 1255 年地震的滑动分别为 11-17 米和 14-22 米，与两次地震之间积累的 10-15 米滑动亏缺相当，这表明沿前缘的大部分变形是由地表破裂地震来调节的。
