Micro Zonation to Earthquake Vulnerability in West Semarang Coastal Indonesia Area Based on HVSR (Horizontal to Vertical Spectral Ratio) Microtremor Method

Research has been carried out to determine the condition of vulnerability to earthquakes in the West Semarang beach region. The research was conducted by measuring the micro tremor signal with the HVSR (Horizontal to Vertical spectral Ratio) method in the area around the West Semarang Beach. Measurements were made by sampling a total of 89 points which were almost evenly distributed in the existing road area. Data collection was carried out in August 2020. The micro tremor signals were measured with a time digital seismograph type 303S, to record a GL 480 data logger, a Garmin III Plus GPS was used to measure the location, and to determine the north direction when installing the seismograph a geological compass was used. For processing, the software Gyopsi, Note Pad++, Excel and Golden Surfer were used. The results of the study indicate that the West Semarang Coast region has a vulnerability to earthquakes grouped into 3 parts, namely the low group, medium group and high group. Village areas with low vulnerability are Randu Garut, Mangkang Wetan, Karang Anyar, Gondorio, Ngalian, Purwoyoso and Mbangaruk. The villages with moderate vulnerability are Tambak Aji, Jerakah and Krapyak. Villages with high vulnerability values are Wonosari, Gondorio, Mangkang Kulon, Tugurejo and Tambak Harjo.