Abstract The seismicity and seismotectonics of Madagascar have been studied using an island-wide distribution of broadband seismic stations. The 28-station MAdagascar-COmoros-MOzambique (MACOMO) array was deployed for a 23-month period between 2011 and 2013. MACOMO data were supplemented by seven temporary stations from the Seismological Signatures in the Lithosphere/Asthenosphere system of Southern Madagascar (SELASOMA) project, ten temporary stations from the Reunion Hotspot and Upper Mantle - Reunions Unterer Mantel project (RHUM-RUM), and 11 permanent stations. A total of 695 earthquakes with magnitudes between ML1 and ML5.3 located within Madagascar were recorded, a new local magnitude scale was developed, and focal mechanisms were determined for 23 well-recorded events. Most of the seismicity is clustered within central Madagascar, forming NW-SE trends in the Ankaratra region and NE-SW trends in the Alaotra and Ankay regions that roughly align with extensional tectonic features. The northern and southern parts of Madagascar also show seismicity clusters that align parallel to existing tectonic features, primarily Precambrian shear zones. Focal mechanisms exhibit a wide orientation of nodal planes, show predominantly normal faulting throughout Madagascar, and provide no evidence for a sharp east-west striking plate boundary between the Lwandle and Somalian plates in the middle of the island. However, a diffuse plate boundary cannot be excluded. We suggest that topographically-generated extensional stresses is the cause of most seismicity, given that significantly fewer earthquakes are located in the lower elevation areas of the island compared to regions of higher elevations. The frequency-magnitude distribution has a b-value of ~1.2 and indicates that events with magnitude ML5 or greater should occur with an average repeat time of ~1.4 years. However, no earthquake exceeding ML6 has been recorded in the last century, suggesting that the frequency-magnitude distribution could be truncated.

中文翻译：

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2011-2013 年全岛 MACOMO 宽带地震阵列的部署揭示了马达加斯加的地震活动性和地震构造

摘要 马达加斯加的地震活动和地震构造已使用全岛分布的宽带地震台站进行了研究。28 站马达加斯加-科摩罗-莫桑比克 (MACOMO) 阵列在 2011 年至 2013 年间部署了 23 个月。 MACOMO 数据得到了来自马达加斯加南部岩石圈/软流圈系统 (SELASOMA) 中的地震特征的七个临时站的补充项目，来自留尼汪热点和上地幔 - 留尼旺Unterer Mantel项目（RHUM-RUM）的10个临时站，以及11个永久站。马达加斯加境内共记录了 695 次震级在 ML1 和 ML5.3 之间的地震，开发了一个新的当地震级，并确定了 23 个记录良好的事件的震源机制。大部分地震活动集中在马达加斯加中部，形成 Ankaratra 地区的 NW-SE 趋势和 Alaotra 和 Ankay 地区的 NE-SW 趋势，与伸展构造特征大致一致。马达加斯加的北部和南部也显示出与现有构造特征平行排列的地震活动群，主要是前寒武纪剪切带。震源机制表现出广泛的节点平面方向，显示整个马达加斯加的主要正断层，并且没有证据表明该岛中部的 Lwandle 和索马里板块之间存在明显的东西向板块边界。然而，不能排除扩散板边界。我们认为，地形产生的拉伸应力是大多数地震活动的原因，因为与高海拔地区相比，位于该岛低海拔地区的地震要少得多。频率-震级分布的 b 值为 ~1.2，表明震级为 ML5 或更大的事件应该以 ~1.4 年的平均重复时间发生。然而，在上个世纪没有记录到超过 ML6 的地震，这表明频率 - 震级分布可以被截断。