The Peel Boundary Fault zone (PBFZ) is the 125 km long, seismically active, northern bounding fault zone of the Roer Valley Rift System (RVRS). The last damaging earthquake along the PBFZ was the Roermond earthquake of 1992. It had a magnitude of Mw 5.3 and no surface rupture. Previous results from two trenching studies located in the central and southeastern parts of the PBFZ provided evidence for two surface rupturing paleo-earthquakes. The largest earthquake had an estimated magnitude of Mw ∼6.8 and a surface rupture length of at least 35 km. As it took place around the Late Pleniglacial – Late Glacial transition a link to glacio-isostatic motions is likely. Results from a new trench situated at the northwestern part of the PBFZ shows evidence for three to four paleo-earthquakes, of which three were surface rupturing. These comprise two normal faulting- and one, younger trans-tensional displacement. The normal faulting events have ∼1 m vertical displacements each, which translate into magnitudes of Mw ∼7. Like the previous results, they occurred during the Late Pleniglacial-Late Glacial transition, at ∼15 ka and ∼ 14 ka. The younger trans-tensional event occurred sometime during the Holocene, pre-dating an unaffected, 13th century man-made paleo-channel on the hangingwall. The potential fourth, non-surface rupturing earthquake is indirectly evidenced by loading deformations of a sand layer and a collapsed brick-wall in the infill of the paleo-channel. Comparison of our trenching results to those from the two previous studies, which were located farther to the southeast along the PBFZ, shows that for one event a correlation is possible. The correlation would indicate a surface rupture length of at least 55 km. Combined, all trenching results indicate that the characteristic maximum rupturing displacement is ∼1 m, and thus that Mw ∼7 is the maximum magnitude of paleo-earthquakes along the PBFZ.

中文翻译：

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罗尔谷裂谷系皮尔边界断裂带西北部分古地震的震级和地表破裂长度

皮尔边界断层带 (PBFZ) 是罗尔谷裂谷系 (RVRS) 长 125 公里、地震活跃的北界断层带。 PBFZ 沿线最近一次破坏性地震是 1992 年的鲁尔蒙德地震。它的震级为 5.3 级，没有地表破裂。先前位于PBFZ中部和东南部的两次挖沟研究的结果为两次地表破裂古地震提供了证据。最大的地震估计震级为 Mw ∼6.8，地表破裂长度至少为 35 公里。由于它发生在晚冰期-晚冰期过渡期间，因此很可能与冰川均衡运动有关。位于 PBFZ 西北部的一条新海沟的结果显示了三到四次古地震的证据，其中三场是地表破裂。这些包括两个正常断层和一个较新的转张位移。每个正常断层事件都有～1 m 的垂直位移，转化为Mw ～7 的量级。与之前的结果一样，它们发生在晚冰期-晚冰期过渡期间，即~15ka和~14ka。较年轻的转张力事件发生在全新世期间，早于上盘上未受影响的 13 世纪人造古河道。潜在的第四次非地表破裂地震是通过古河道填充物中沙层和倒塌砖墙的荷载变形间接证明的。将我们的挖沟结果与之前两项研究的结果进行比较（这两项研究位于沿 PBFZ 的东南部更远的地方），表明对于一个事件，可能存在相关性。该相关性表明表面破裂长度至少为 55 公里。综合起来，所有挖沟结果表明，特征最大破裂位移为~1 m，因此Mw~7是PBFZ沿线古地震的最大震级。