bob@uhmanoa.UUCP (02/05/87)
The Hawaiian islands continue to feel some aftershocks after Tuesday's magnitude 5.2 quake eipcentered 50 miles west of the big island. The aftershocks---largest being about 3.9 on the Richter scale, the rest hovering around 3.0---went have been going on for a couple of days. After the first quake at 1622 HST Tuesday, the 3.0 or greater smaller quakes were recorded at 1745 Tues, 0315, 0542, 0756, 1055 and 1236 Wednesday. Considerable lower-level activity also shows up on the seismographs. Unlike the normal, smaller earthquakes which occur regularly on the big island of Hawaii---the Hawaii Volcano Observatory weekly report routinely plots epicenters of earthquakes > 3.0, but quakes greater than 4.0 are rare---the 5.2 quake and associated aftershocks are not related to volcanic activity. Instead, these quakes are probably due to tectonic side effects of isostatic equilibrium adjustments as the islands settle. It's a bit too soon to correlate sea level measurements, but I'm fairly sure that they will show that a couple of the islands settled a few mm in the process...the long-term rate being about 13 cm per century. -- Bob Cunningham bob@hig.hawaii.edu