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Lombok_Earthquakes_20180823

Three minor events (R4.5 and R5.1 on 8/21 and the R4.9 on 8/22) in the last couple of days. That’s not worthy of inclusion in the news cycle. But geological time is different than news time. Each circle represents an earthquake in the last 4 weeks – 90 events is a lot in such a small area (perhaps 1000 square miles) in less than one month. Without a major event like a Richter 8.5, for example, there should never be two Richter 6.9s so close in time and space.  The Richter 6.3 and 6.4 are too strong to be classical prime aftershocks, and the two Richter 5.9s are out of profile as well. Currently, the spread of events to Sumbawa island is not worrying many people as western Sumbawa is not target-rich. Likewise, a tsunami rumbling through either the strait to the west or the strait to the east is unlikely to cause major damage – neither strait hosts a major city, and neither strait is used to transport valuable commodities. Cynically, very few people not on Lombok would care  much if a major earthquake, with or without tsunami, struck Lombok.  Even a somewhat impressive VEI=4 eruption [between 0.1 and 1.0 cubic kilometers of ejecta; plume heights between 10 and 25 kilometers; happens about once every 25 years world-wide; probably pyroclastic flows, lava, hot ash) from Rinjani (on Lombok) or Tambora (on Sumbawa) or Agung, Batur or Bratan (on Bali) or perhaps some new volcano would only cause local damage. The eruption of Mount Saint Helens in Washington State in 1980 was a VEI=5 event, while Pinatubo 1991 is now commonly described as a VEI=6. Tambora (on Subawa) 1815 and Samalas (on Lombok; now known as Rinjani)  in 1257 were VEI=-7 events that impacted the climate of the our planet.

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