Italian Earthquake, M5.0
Further west along the margin of the Eurasian plate, the dominant tectonic setting is subduction rather than collision, as the remains of the Mediterranean are subducted by northward movement of the African plate. However, the resulting tectonic pattern is highly complex and includes both compressive and extensional forces within the Mediterranean Basin.
A more detailed structural geologic map can cause as much confusion as clarification, but it appears that the tremor, which occurred on the northern edge of the folded Apennine Mountains on January 25, may have been the result of movement along a thrust fault due to the collision of the Apennines with a sliver of continental crust to the north. Although major earthquakes are rare, a map of seismicity since 1990 shows many hundreds of shallow, small-magnitude tremors across the region.
The USA’s Largest Earthquake This Week
Surprisingly, the entire U.S.A. – including Alaska and California – were without a tremor of ≥M5.0 this past week. The largest seismic event recorded in the mainland states (second only to a marginally larger tremor in earthquake-prone Alaska) was a M4.1 in tectonically-stable Texas on January 25, 2013. In the absence of any plate margins, it seems likely that this event was the result of local faulting.
Texas Quake Most Notable of the Week
The relatively minor tremor in Texas is probably the most notable event of the week. Texas contributes only one event to the USGS historic earthquakes list for the U.S.A. (compared to over a hundred for California) and that quake, the largest in the state, was of a relatively small magnitude, M5.8. So even in a quiet week, the Earth is still capable of producing the odd seismic surprise.
United States Geological Survey. Real time earthquake map. (2013). Accessed 29 January 2013.
United States Geological Survey. Historic earthquakes in the USA. (2013). Accessed 29 January 2013.
Yeats, R. Active Faults of the World. (2012). Cambridge University Press.
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