Smithsonian Institution Global Volcanism Network Bulletin v. 19, no. 8, August 1994 Merapi (Indonesia) Two new broad-band seismometers detect long-period pulses and tremor Merapi central Java, Indonesia (7.54xS, 110.44xE) All times are local (= GMT + 7 hours) Two STS2 broad-band seismometers were deployed on 27-29 July by collaborators of the Geophysical Laboratory of the GMU and Martin Beisser of GFZ-Potsdam. The researchers investigated signal coherency at different points on the volcano to find suitable sites for a multi-station seismic array that will make permanent records at a 50-Hz sampling rate. The researchers measured Merapi seismicity at a base station located at Klathakan (1.8 km WNW of the summit between 1,200-1,300 m elevation), the site of a seismic station for the last 8 years. The second station was mobile and GPS-equipped; however, for the following comparisons and discussion the mobile site remained 400 m N of the base station. Figure 5 shows amplitude data for 3-components of volcanic shock from the mobile station. The volcanic shock event that began at 1750 and 37 seconds on 27 July is here termed Event A. Figure 6 shows the arriving signals and allows for a visual comparison of the coherency in the vertical component (top 2 plots), and two orthogonal horizontal components (lower 4 plots). From visual inspection, the best coherency appeared in the vertical-component data. Some other types of events received appeared to show less coherency between the two sites. Figure 7 shows 3 components of a previously undetected tremor type, a tremor preceded by or superimposed on a long-period pulse. On the record, the interval of greatest short-period amplitude came after the pulse's maximum. Examples of this kind of tremor were seen 3 times in 12 hours. Whether these events are common on Merapi and elsewhere still remains uncertain. Merapi, one of the most active volcanoes in Indonesia, sits immediately N of the large city of Yogyakarta; at least 50,000 people live adjacent to its SW slope. The stratovolcano has an exposed, summit lava dome, the source of abundant glowing blocks that continue to tumble down its SW slope. In historical time, instability of the growing dome has led to nuees ardentes that have caused many fatalities, disasters described in many popular books on volcanology. Information Contacts: Martin Beisser, GeoForschungs-Zentrum-Potsdam, Telegrafenberg A31, H117, 14473 Potsdam, Germany (Email: firstname.lastname@example.org); Arnold Brodscholl, Geophysics Laboratory, Gadjah Mada University (GMU), FMIPA-UGM, Sekip Unit III, P.O. Box BLS 21, Yogyakarta 55281, Indonesia (Email: email@example.com).