Matata Quake Swarm Continues to Decline

The number of earthquakes reported on the Geonet website as associated with the Matata earthquake swarm declined slightly during June 2007. However, databases which include earthquakes which would not have been felt, have shown a greater decline in recorded events.

The current earthquake swarm near Matata commenced in December 2006. Activity reached a peak reported rate of 30 events during March, with the strongest quakes reported during May. During June, reported activity declined only slightly, with slightly fewer earthquakes reported and the strongest quake declining to magnitude 3.8.

Earthquakes reported on the Geonet website for the current Matata swarm are as follows:

December 2006 4 events, magnitude 2.8 to 3.4
January 2007 6 events, magnitude 2.8 to 3.1
February 2007 10 events, magnitude 2.5 to 3.7
March 2007 30 events, magnitude 1.9 to 4.1
April 2007 23 events, magnitude 2.6 to 4.0
May 2007 18 events, magnitude 2.4 to 4.2
June 2007: 15 events, magnitude 2.5 to 3.8

Following the magnitude 4.2 earthquake on May 3rd, Geonet issued a preliminary analysis on May 11th, comparing the 2007 swarm with a similar swarm nearby in 2005.

The 2005 Matata earthquake swarm commenced activity in January, peaking in April and gradually declining from late June to early December. The beginning of activity was more abrupt than the current swarm, and more than 1000 quakes had been identified by year’s end.

The 2007 swarm began more steadily with the number of individual earthquakes increasing with time. By May 11th, 700 earthquake events (most too small to have been felt) had been analysed by seismologists at GNS Science.

At the time the preliminary report was released, it was thought that the two swarms were similar in terms of the expected duration of the swarm, the number of earthquakes and the total energy release. It was expected that the swarm would gradually die away over several months without any significantly larger events.

Geonet’s databases contain nearly 90 shallow earthquakes identified near Matata during June, compared with about 160 for May. This is considerably more than reported on the website, as only earthquakes actually or likely to be felt are reported in detail.

[Compiled from data provided by Hazardwatch and the Geonet project and its sponsors EQC, GNS Science and FRST.]

One Response to “Matata Quake Swarm Continues to Decline”

  1. Chris says:

    I bet the residents of Matata are grateful it’s subsided…

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