Scientists watch 'slow quake'
POSTED: Thursday, October 02, 2008
| This story has been corrected. See below. |
HILO » Shortly after Father's Day last year, scientists studying the area southeast of Kilauea Volcano's summit discovered a “;slow earthquake”; and, for the first time ever, saw the mechanism that probably caused it, according to a paper published in Science magazine.
For about 10 years, geologists have known about slow earthquakes - big underground earth movements taking place so slowly that they do not go bang. The causes were “;unresolved,”; University of Hawaii researcher Ben Brooks and others said in the Aug. 29 Science article.
Beginning Father's Day, June 17, 2007, they saw a cause. A shallow, 1-yard-wide arm of magma pushed underground from Kilauea's summit toward the southeast. The underground pressure it created was the trigger for what came next.
Fifteen to 20 hours after the magma push started, about five miles deep in ancient rocks, a large chunk of the Big Island started creeping and grinding slowly toward the sea. That qualified it as an earthquake, but since there was no big snap, no one noticed.
Even with several dozen instruments positioned to record this kind of thing, the science team needed a few days to sort out what was happening, Brooks said.
Understanding earth movement five miles underground that they could not see or feel called for interpretation of instrument readings. In particular, radar images of the ground taken from a satellite showed some new surface bulges and low spots.
The team applied some math. The best explanation was a slow quake.
The scientists were happy to see the cause and effect between the magma and the quake, and their Science article stopped there.
Brooks was reluctant to link the discovery to a topic his team had discussed in early 2007, a prediction that a slow quake would take place in March in this same area. That prediction was based on four previous quakes which took place almost like clockwork, every 774 days, plus or minus a week. The cause for those earlier slow quakes is still unknown.
The predicted March quake did not happen, but the June quake was in the same area and just a bit late.
Was the June quake the answer to the March prediction? “;It's not clear how this fits in,”; Brooks said.
“;Is another one going to be happening in 774 days?”; he wondered. “;We'll be looking.”;
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