Saturday, May 20, 2006

A quick update: mountain’s smoky again today, and lava’s still shooting out regularly. 44 times today, according to Subandrio. I talked to him earlier in the week about the mountain. He seems sleep deprived and punchy. Here’s an excerpt from the interview. I should add that his boss, the head of the volcanology office, has been sick since Tuesday. His boss is much better with English, but not nearly as fun.

Click here for an interview with Subandrio from Thursday.

And here's the center's website. Great info, and some fun background. Gotta love the glossary:

The classification of Merapi seismic events has been improved since the 1984 eruption. Merapi seismic signals are distinguished into six (6) types:

VA event. It is the deepest tectonic-like volcano-seismic events known in Merapi volcano. The hypocenter depth ranges from 2 to 5 km below the summit. The P and S phases are clearly separated. Dominant frequency recorded at 2625-m altitude is between 5 to 8 Hz. Amplitude is comparable between all stations because the source is about the same distance from all the stations.

VB event. This type is similar in their frequency to the VA events. Due to the close proximity of the hypocenter, the S phase is difficult to accurately identify. The depth of hypocenter is usually less than 1.5 km from the summit.

MP event. The term "MP" ("manyphases") was proposed firstly by Shimozuru et al. (1970) to describe seismic events that occur during the lava dome formation. For a given amplitude, MP event has a longer duration than that a V-type event. Further away from the summit, the amplitude is strongly attenuated. The dominant frequency is about 3 to 4 Hz.

LF event. This is a low frequency seismic event of about 1.5 Hz. The frequency content is constant from one station to others. The seismograph positioned close to summit records the event with a much higher amplitude than at more distant stations indicating that it has a shallow origin (less than 1 km).

Tremor. Tremor is easy to distinguish from other seismic events because of its duration. Its frequency content is similar to that of LF event.

Guguran. This is a local term for landslide or rockfall originating from the lava dome. On seismogram signal associated to rockfall has a high frequency content and a long duration. The duration of signal is about equal to the duration of rockfall process.


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