Matata Swarm Gains Momentum

The swarm of earthquakes which has been occurring near Matata in the Bay of Plenty increased in activity during March 2007.

Data published on the Geonet website shows that the number and size of the earthquakes reported near Matata increased dramatically last month.

The swarm commenced in December 2006 with one 2nd magnitude and three 3rd magnitude quakes being reported by Geonet, a total of four events.

During January, six quakes were reported, two 2nd magnitude and four 3rd magnitude.

Ten events were reported during February, five were 2nd magnitude and five were 3rd magnitude.

During March thirty earthquakes were reported within 10 km of Matata. One was magnitude 1, six were magnitude 2, twenty-one were magnitude 3 and two were magnitude 4.

The largest reported quake in the swarm struck early on the afternoon of Friday 30th March. The magnitude 4.1 earthquake was felt from Ohauiti to Whakatane and at Lake Rotoiti and Kawerau to the south, resulting in 101 felt reports on the Geonet website.

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

5 Responses to “Matata Swarm Gains Momentum”

  1. Chris says:

    Makes one wonder how long this is going to go for….

  2. Darren McManaway says:

    I note these events seem to be getting shallower with time…

    Any reasioning for this?

  3. Ken says:

    Good question. It sent me scurrying off to crunch some numbers.
    The key is – are they getting shallower with time?
    Data published by Geonet on Matata swarm events is as follows –
    Dec 2006. 4 events. depth 3 km (1), 4 km (1), 5 km (2)
    Jan 2007. 6 events. depth 2 km (1), 5 km (5)
    Feb 2007. 10 events. depth 3 km (1), 4 km (3), 5 km (4), 6 km (1), 7 km (1)
    Mar 2007. 30 events. depth 1 km (1), 2 km (5), 3 km (1), 4km (2), 5 km (17), 6 km (3), 8 km (1)
    Apr 2007 to date. 10 events. depth 1 km (1), 2 km (7), 5 km (1), 6 km (1).

    Possible answers –
    1.They ARE getting shallower with time.
    2.Data skewing. Unlike USGS which publishes quakes above a fixed magnitude, Geonet tends to publish earthquake data for events likely to be, or actually, felt. Residents will be more aware of the swarm and hence more likely to report shallower events which will appear on the website.
    3.GNS Science has probably deployed additional seismic instrumentation in the area which will increase their precision in locating quakes by depth and location.
    I’ll make some enquiries and get back with a comment or an article in the next day or so.

  4. Ken says:

    Enquiries show that the apparent trend toward shallower events is due to increased analysis using more seismic stations. See latest post on Wild Land today (April 11th)

  5. Darren McManaway says:

    Thanks for that Ken – that explains a lot.

    Great site!

    🙂

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