Locating tremor and shock sources recorded at Bromo Volcano

Abstract

During a phase of high eruptive activity, as well as high tremor activity, seismic signals were recorded at Bromo Volcano (East Java) for almost three months in 1995. The signals generated by the volcano cover a broad frequency range including long period signals with frequencies between 10 and 100mHz, tremor signals at about 5Hz and volcanic shocks with frequencies up to 25Hz. Seismic signals from volcanoes, especially tremors, have been classified and categorized in different ways, but interpretation has always been limited by the difficulties in determining even approximate source locations. Volcanic tremor lacks an emergent first onset, while the complex structure of the volcano makes it difficult to determine other phases from shock signals than first arrivals.If the volcanic signal has been recorded in at least two stations, the location of its seismic source can be estimated using a grid search method if we assume the source radiates isotropically in a homogeneous medium.Applying the grid method to data recorded at Mt. Bromo, we determine the locations of the sources of tremor and shock signals. The sources for both types of signals are located in the northwestern part of the crater, near the open vent and also near the source of long period signals (Gottschämmer, 1999. Annal. Geofis. 42 465–481).