Smithsonian Institution Global Volcanism Network Bulletin v. 20, no. 8, August 1995 Rabaul (Papua New Guinea) Intracaldera cones quiet, but nearby earthquake triggers local seismicity Rabaul New Britain Island, Papua New Guinea 4.27 S, 152.20 E; summit elev. 688 m All times are local (= GMT + 10 hours) Although Rabaul remained quiet in August, the region was subjected to a strong tectonic earthquake (Ms 7.8) followed by associated aftershocks (see Earthquakes, below). The earthquake struck on 16 August centered ~260 km SE of Rabaul. In Rabaul the earthquake struck at 2027 with a modified Mercalli (MM) intensity of V, causing some minor landslides and the collapse of a few buildings. The earthquake triggered noteworthy responses at the caldera. On 16 August there were 24 high-frequency events, and, as late as 23 August, 3-9 additional events/day; in July there were 7 high-frequency earthquakes (M <1). On 22 August, one event was felt by residents. With an approximate magnitude of ML 2.8, this was the first felt caldera earthquake since the early phase of Rabaul's September 1994 eruption. These high-frequency earthquakes occurred mostly in the NE part of the caldera (Namanula Hill area). In contrast, throughout the period of heightened seismicity the number of low-frequency earthquakes remained low, peaking on 30-31 August at 10 and 26 events, respectively. For comparison, during July low-frequency events occurred 11 times. The August low-frequency earthquakes appeared to originate from within or just outside the N caldera area. During the first half of the month ground deformation remained below the measurable level. Following the Ms 7.8 earthquake, electronic and water-tube tiltmeters recorded offsets as large as 90 microradians. The offsets suggested subsidence in the central part of the caldera with the outer rim remaining stationary. As of 15 September, adequate elevation data were unavailable to confirm the pattern of offset seen in the deformation data. Information Contacts: Same as for Manam.