Abstract Repeating earthquakes are key evidence for understanding earthquake recurrence and help improve long-term seismic risk assessment. In 1986 and 2016, two Ms6.4 earthquakes occurred in Menyuan region, near the middle segment of Qilian-Haiyuan fault zone, NE Tibetan Plateau. Long period waveforms of the two events at teleseismic stations show high degree of similarity, however, previous solutions on earthquake location and focal mechanism show remarkable discrepancies, especially for the 1986 event, as well the ruptured faults also remain ambiguous. In this study, we determined the source parameters of these two earthquakes, including the relative location, focal depth, focal mechanism, source duration and rupture directivity. The results show that two earthquakes are thrust events in shallow crust and are located within 15 km, and the 2016 earthquake ruptured down-dip for ~6 km along the southwest dipping plane. Combing the source parameters, geological data and deep seismic-reflection profiles, we infer that these two earthquakes occurred on the same secondary fault of Lenglong Ling fault (the middle segment of Qilian-Haiyuan fault), but they ruptured on different sections of the fault. Although the two events are probably not repeating earthquakes of Qilian-Haiyuan fault zone, the seismic risk of ~M6 thrust earthquake on these secondary faults and even larger strike-slip earthquake on Lenglong Ling fault are not negligible based on the source parameters and ten-year GPS observations.

中文翻译：

---

基于震源参数的祁连-海原断裂带（青藏高原东北部）2次Ms6.4门源地震重复性检验

摘要 重复地震是理解地震复发的关键证据，有助于改进长期地震风险评估。1986年和2016年，青藏高原东北部祁连-海原断裂带中段附近的门源地区发生了两次Ms6.4地震。远震台站两次事件的长周期波形具有高度相似性，但以往的地震定位和震源机制解显示出显着差异，尤其是1986年的事件，断裂断层也仍然模糊不清。在这项研究中，我们确定了这两次地震的震源参数，包括相对位置、震源深度、震源机制、震源持续时间和破裂方向性。结果表明，两次地震为浅地壳逆冲事件，均位于15公里以内，2016 年的地震沿西南倾斜面向下倾斜了约 6 公里。结合震源参数、地质资料和深部地震反射剖面，我们推断这两次地震发生在冷龙岭断裂（祁连-海原断裂中段）的同一次断层上，但在断裂的不同断面破裂. 虽然这两次事件很可能不是祁连-海原断裂带的重复地震，但从震源参数和十次地震的震源参数来看，这些次生断层发生~M6逆冲地震以及冷龙岭断裂发生更大走滑地震的地震风险也不容忽视。年 GPS 观测。我们推断这两次地震发生在冷龙岭断裂（祁连-海原断裂中段）的同一次断层上，但在断裂的不同断面破裂。虽然这两次事件很可能不是祁连-海原断裂带的重复地震，但从震源参数和十次地震的震源参数来看，这些次生断层发生~M6逆冲地震以及冷龙岭断裂发生更大走滑地震的地震风险也不容忽视。年 GPS 观测。我们推断这两次地震发生在冷龙岭断裂（祁连-海原断裂中段）的同一次断层上，但在断裂的不同断面破裂。虽然这两次事件很可能不是祁连-海原断裂带的重复地震，但从震源参数和十次地震的震源参数来看，这些次生断层发生~M6逆冲地震以及冷龙岭断裂发生更大走滑地震的地震风险也不容忽视。年 GPS 观测。