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Characteristics of the Seismic Clusters Bounding the Ramu-Markham Fault Zone, Eastern Papua New Guinea
Journal of the Geological Society of India ( IF 1.3 ) Pub Date : 2021-01-01 , DOI: 10.1007/s12594-021-1621-6
George Noho , Manoj Mukhopadhyay , Basab Mukhopadhyay , Diptansu Sengupta

The regionally extensive Ramu-Markham-Fault-Zone (RMFZ) in Papua-New-Guinea (PNG) passes through the seismically-active hinterland of the Bismarck subduction zone in SW-Pacific. The seismicity map for 400km segment of RMFZ shows that higher magnitude earthquakes mainly originate in four spatial clusters (I–IV), asymmetrically disposed from in-land to offshore on either side of RMFZ. The cluster III have produced the 2019 Buloloearthquake (Mw 7.1). The spatial and temporal characters for all four seismic clusters was estimated by: (i) b-value based on maximum-likelihood method; (ii) expected maximum magnitude (Mw) by Gumbel extreme value statistics and surface rupture length; and (iii) the Hurst coefficient (K) and Hurst plot. Hurst plots on sequential seismic moments in the clusters illustrate an alternating positive and negative sloping moment-release pattern over progressive time-period that corresponds to low and high b-values respectively. The regional stress pattern on north and south of RMFZ and for four seismic clusters are analysed by inversion of CMT focal-mechanism data. The result unravels a significant change in regional stress pattern across the RMFZ: (i) a pure-compressive stress regime corresponding to clusters I and II in the ‘PNG Highlands’ that gradually changes to transpressive in the off-shore cluster IV along north of RMFZ, and (ii) the regional stress pattern for earthquakes south of RMFZ including cluster III shows absence of any particular stress orientation and causative faults are randomly oriented. This leads to the presentation that RMFZ is a deep penetrative fault, rather than a crustal ramp fault restricted to 11–18km depth as advocated in literature.

中文翻译:

巴布亚新几内亚东部 Ramu-Markham 断裂带边界地震群的特征

巴布亚-新几内亚 (PNG) 区域性广泛的拉穆-马卡姆-断层带 (RMFZ) 穿过西南太平洋俾斯麦俯冲带的地震活跃腹地。RMFZ 400km 段的地震活动图显示,较高震级的地震主要起源于四个空间簇(I-IV),从RMFZ 两侧的内陆到海上不对称分布。集群 III 产生了 2019 年布洛洛地震(Mw 7.1)。所有四个地震簇的空间和时间特征估计为: (i) 基于最大似然法的 b 值;(ii) 根据 Gumbel 极值统计和表面破裂长度的预期最大震级 (Mw);(iii) Hurst 系数 (K) 和 Hurst 图。簇中连续地震矩的赫斯特图说明了在渐进时间段内交替的正负斜矩释放模式,分别对应于低 b 值和高 b 值。通过CMT震源机制资料反演,分析了RMFZ南北和四个地震群的区域应力格局。结果揭示了整个 RMFZ 区域应力模式的显着变化:(i)对应于“PNG 高地”中的簇 I 和 II 的纯压缩应力状态,在沿RMFZ 和 (ii) RMFZ 以南地震的区域应力模式,包括第三类,显示没有任何特定的应力方向,并且成因断层是随机定向的。
更新日期:2021-01-01
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