Surface Geology Analysis on the Relationship between Fault Creep and Overpressure in Grobogan, Central Java, Indonesia

Abstract

The Grobogan Regency is a significant location for oil and gas exploration due to its proximity to active oil and gas fields. Geologically, this area is intersected by the Kendeng thrust fault and exhibits several surface manifestations of mud volcanoes near the fault. However, there have been limited studies examining the activity of the Kendeng thrust fault and its relationship to overpressure and earthquakes, which could affect oil and gas exploration and natural disaster mitigation in the region. This paper focuses on utilizing surface geological mapping data and Interferometric Synthetic Aperture Radar (InSAR) data to analyze the relationship between fault creep and overpressure manifestations in Grobogan, Central Java. While continuous research on fault creep has been conducted since the 1960s on the San Andreas fault in the United States, there has been a lack of continuous research on onshore fault creep in the Northeast Java Basin or Kendeng Basin, particularly in the Grobogan area. This region, known for its abundance of active mud volcano manifestations, is predominantly characterized by marl and clay lithology. It represents a warm basin environment that is prone to overpressure and ideal for fault creep occurrences.To investigate further, fluid, gas, and mud samples were collected from the mud volcanoes, along with rock samples from the surrounding area, for comprehensive laboratory analysis. The integration of these sample analyses aimed to determine the correlation between the activity of the Kendeng thrust fault creep and the subsurface overpressure conditions. While this study observed several indications of creeping in the vicinity of InSAR anomalies, the exact location of the creeping fault plane could not be definitively determined. The Kendeng thrust fault exhibits the three main factors necessary for initiating fault creeping. The fault segment’s extremely slow creeping may be linked to the activity of the mud volcanoes, as indicated by the results of fluid, gas, and rock sample analysis. The findings of this research hold potential for informing the development of oil and gas fields, as well as enhancing the mitigation of natural disasters associated with oil and gas exploration and earthquakes in the region.