ruaumoko: 2009 June -July Mt. Tihia Tokaanu swarm

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2009 June -July Mt. Tihia Tokaanu swarm

The Mt. Tihia/Tokaanu Swarm of June/July 2009 was basically broken into 2 separate sequences north and south of the summit of Mt. Tihia.
The first swarm started on 11th June with 2 micro quakes and another on the 12th, but on the 14th the area really started to show evidence of activity in the southern flanks of the mountain. There were no quakes in the area on the 21st June, so I took the last quake on the 20th June at 14:18:23.8 as the break point before the 2nd sequence started on the 22nd more towards the northern base of the volcano and Tokaanu.
The 2nd sequence ran through to July 10th when activity petered off.
There were no quakes on the 4th, 6th and 7th July, but it would be hard to deny that this is one big swarm, broken down into 3 sequences or bunches, even with those gaps.

If you take in the earlier events of late May further south near Lake Rotoaira, from May 30th to June 8th at the northern end of Lake Rotoaira, which had 105 events and add them to the 2 other sequences ( based on date and location) that brings the total to 849 events between May 30th and 10th July in the area.
The map below shows all the events May 30th and 10th July using a combination of breaks in the dates (when there were no quakes) and also as the majority of the events moved as a group, to separate it down to 3 main bunches or sequences.
locations of events May 30th to July 10th

locations of events May 30th to July 10th

Data for the first swarm can be viewed in detail on the page. Rotoaira/Rotopounamu swarm

The second part of the overall swarm (or the first part of the Mt.Tihia /Tokaanu part) started on 11th June and ran through to 20th June, the map below shows all the events of this period.
First map shows location and magnitude and the second map breaks the swarm down on a daily basis ( magnitudes are not shown)
locations of events June 11th to June 20th

locations of events June 11th to June 20th

locations of events June 11th to June 20th by date

1 comment:

SmithyDecember 27, 2009 at 12:50 PM
This has the potential to make the crater lake look like a storm in a tea cup.
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Earthquake Swarms

Earthquake swarms are events where a local area experiences sequences of many earthquakes striking in a relatively short period of time. The length of time used to define the swarm itself varies, but the United States Geological Survey points out that an event may be on the order of days, weeks, or months. They are differentiated from earthquakes succeeded by a series of aftershocks by the observation that no single earthquake in the sequence is obviously the main shock. Earthquake swarms are one of the events typically preceding eruptions of volcanoes

Earthquake Aftershocks

An aftershock is an earthquake that occurs after a previous earthquake (the main shock). An aftershock is in the same region of the main shock but is always of smaller magnitude strength. If an aftershock is larger than the main shock, the aftershock is redesignated as the main shock and the original main shock is redesignated as a foreshock. Aftershocks are smaller earthquakes formed as the crust around the displaced fault plane adjusts to the effects of the main shock

Aftershocks are dangerous because they are usually unpredictable, can be of a large magnitude, and can collapse buildings that are damaged from the mainshock. Bigger earthquakes have more and larger aftershocks and the sequences can last for years or even longer especially when a large event occurs in a seismically quiet area; see, for example, the New Madrid Seismic Zone, where events still follow Omori's law from the mainshocks of 1811–1812. An aftershock sequence is deemed to have ended when the rate of seismicity drops back to a background level; i.e., no further decay in the number of events with time can be detected.