RABAUL UPDATE 9/26/94 1500 PDT

The following is taken from a telephone conversation between scientists at CVO and Chris McKee and Rod Stewart of the Rabaul Volcano Observatory (RVO).

Current situation:

Vulcan is no longer erupting. No portion of Vulcan has collapsed. Tavurvur is still erupting an ash plume. There is an ashy haze over Rabaul town. Seismicity is much decreased-- now at about the limit of RSAM (Real Time Seismic Amplitude) detection.

RVO no longer has the ability to locate earthquakes. Three seismic stations remain in operation. The other stations have been incapacitated by tsunamis, vandalism, or heavy ash fall.

About 40 mm of fine powdery ash has fallen at RVO. The airport received about 0.5 m of ash, and the airfall thickens rapidly towards Matupit Island.

Precursors:

At 0300 local on Sunday 9/18 a magnitude 5.1 earthquake occurred beneath the harbor. An aftershock sequence from this event merged into an intensifying swarm of high-frequency (A- type) earthquakes. Peak intensity of this swarm occurred around midnight Sunday with about 2 felt events per minute. The earthquake swarm tapered off slightly toward moming. By 0600 Monday, the eruption had begun. Thus only 27 hours of unusual seismicity preceded the eruption.

Inspection of seismograms since the onset of the eruption revealed that several L-P events had occuffed in the 12 hours prior to the magnitude 5.1 earthquake.

CVO/VDAP response:

CVO/VDAP will send three volcanologists, a seismic system consisting of telemetered seismic stations and a PC-based data- acquisition and analysis system, several telemetered tiltmeters and other deformation monitoring instrumentation on Wednesday 9/28.