The 1922 Peninsula Malaysia earthquakes: Rare intraplate seismicity within the Sundaland Block in Southeast Asia

Seismic hazard in the southern Malay Peninsula located within the Sundaland block in Southeast Asia is poorly understood. The paucity of historical earthquakes and low-magnitude instrumented seismicity has led to the assumption that this region is largely aseismic. We question this point of view by reassessing historical seismicity in this region and, in particular, a pair of moderate earthquakes in the 1920s. The first of these struck on 31 January 1922 at ≈9:10 a:m: local time (LT) for which we estimate an intensity magnitude (M_I) ≈5:4, and for the second earthquake on 7 February 1922 at ≈12:15 p:m: LT, we estimate M_I≈5:0. We also identify at least 34 felt earthquakes between 1803 and 1950 that were potentially local within the Sundaland block. These include a very widely felt shock (or set of shocks) on 26 June 1874 that was felt in parts of Borneo, Java, and Sumatra. The discovery of these earthquakes challenges the tectonic stability of the Malay Peninsula and the stable interior of the Sundaland block. The record of historical seismicity in this region relies heavily on European sources, and we recommend locating and consulting indigenous sources to improve the current understanding of regional seismic hazard. We also underscore the need to evaluate the impact of ground motions from rare local earthquakes on the extant building stock and on transportation infrastructure that are otherwise relatively immune to the long-period effects of distant earthquakes commonly felt in the Malay Peninsula.