Research Article Characteristics of Earthquake Hazards in Jailolo, West Halmahera, Indonesia: An Analysis of b Values and Site Dynamics

Jailolo, the capital of West Halmahera Regency, faces earthquake risks due to its proximity to a Jailolo volcano and a double subduction zone in Eastern Indonesia. This study is aimed at investigating the seismic hazard characteristics in Jailolo through the analysis of statistic and signal parameters. Analyzing seismic hazard characteristics in this region is crucial for assessing earthquake risks and understanding how local soil conditions influence ground shaking. Earthquake catalogs from several databases spanning from 1970 to 2018 were utilized. Additionally, 40 locations around Jailolo were surveyed using a shortperiod seismometer to gather microtremor data. The earthquake catalogs underwent b value analysis using the maximum likelihood method, while microtremor data were examined for f0and A0using the horizontal-to-vertical spectrum ratio (HVSR) method. VS30profiles were derived using the H/V curve inversion method. The b value characterizes earthquake size distribution, HVSR evaluates ground properties, especially the shallow subsurface, and VS30represents the time-averaged shear wave velocity in the upper 30 m of the Earth’s surface. The findings revealed the average b value around Jailolo is 1.36 with a 15% deviation, categorizing the area as earthquake prone and volcanic. The values of f0and A0ranged from 0.536 to 2.44 Hz and 8.97 to 21.2, respectively. The results of f0and A0suggested that the Jailolo area is predominantly characterized by thick sediment. The H/V curve analysis provided a VS30profile ranging from 109 to 460 m/s, indicating that the area is dominated by sediment consisting of stiff soil, very dense soil, and soft rock. In conclusion, Jailolo is highly prone to earthquakes due to its seismic and volcanic activity, supported by soil characteristics that can amplify seismic waves and increase ground shaking intensity during earthquakes. These findings stress the need for long-term seismic monitoring and community involvement to mitigate seismic risks.