Microtremor analysis around Jari mud volcano, Bojonegoro

Abstract

The earthquake that occurred in the Mount Pandan area in 2016 is thought to have triggered the emergence of a mudflow mixed with water and gas. The research area is in the Kendeng Zone with a complex geological structure. In this zone, there is a very fast sedimentation process so the buried material is not fully compacted. In this study, measurements were made of 6 microtremor data points around Jari Mud Volcano, Bojonegoro, East Java, Indonesia. Furthermore, the data obtained were processed using the HVSR analysis method. HVSR analysis is a method of processing microtremor signals to determine soil characteristics based on information on natural frequency values and its amplification. The result shows the natural frequency parameter and its amplification is slightly variated around Jari Mud Volcano, caused by sedimentary depth variation and/or the presence of existing rock. Based on 6 processed data, the natural frequency values range from 1.9 to 9.1 Hz. Meanwhile, the amplification value ranges from 2.6 to 4.4. Based on the amplification value, the research area is classified as low and medium amplification zones (low value dominance). This is because the amplification value is related to geomorphological conditions, in which the research area is located in the mountains and is composed of volcanic sediments.