Western Mediterranean Earthquake July 7, 2011 Recorded at Keele, UK

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Jul 082011
 
20110707 Mediterranean Sea

After a large earthquake of the other side of the world, this time an earthquake a little closer to home with a magnitude 5.3 tremor occurring in the Western Mediterranean Sea between France and Corsica. There seems to be not much information on this ‘quake. The EMSC indicate that it has a thrust fault mechanism with a northeast-southwest strike. It also appears to be in a region of little recent seismicity.

This event needed a bit of high-pass filtering to get it to stand out from the background noise but the result is clear enough to identify the P-, S-, and Rayleigh wave arrivals and obtain an epicentral distance of about 11-12° from the travel-time curves. Events closer than about 30° tend to have complex waveforms as they are travelling mostly through heterogeneous crust rather than homogeneous mantle.

More information:
USGS
EMSC
Earthquake-Report

Kermadec Islands Earthquake July 06, 2011, Recorded at Keele, UK

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Jul 072011
 
20110706 Kermadec

This is the recording of the large Kermadec Islands earthquake of June 6, 2011, recorded on our schools seismology SEP seismometer here at Keele University in the UK.

Being at an epicentral distance of 155.3° from the epicentre, the first arrival is the PP phase as the direct P-wave is obstructed by the core.

The event is somewhat unusual as one would normally expect an earthquake of this magnitude along a subduction system to be a low-angle thrust event along the plate boundary between the Pacific and Australian Plates dipping gently to the west. However, the CMT focal mechanism determined is one of a normal fault. This event is right on the trench so it was possibly caused as the subducting Pacific Plate is forced to flex in order to subduct beneath the Australian Plate. The historical data show a magnitude 6.6 event from 2008, also on the position of the trench with a similar mechanism.

The ‘quake seems to have caused a ~1m tsunami wave locally but a more regional tsunami alert was cancelled.

Further details from the USGS.

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