ABSTRAKSejarah kegempaan Jawa antara tahun 1981 hingga 2014 mencatat bahwa Daerah Istimewa Yogyakarta telah dilanda gempabumi merusak sebanyak 4 kali dan ratusan gempabumi terasa. Penelitian ini bertujuan mengkaji zona percepatan tanah maksimum (PGA) dan intensitas gempabumi berdasarkan data historis kejadian gempabumi dari tahun 1981-2014. Perhitungan percepatan tanah maksimum menggunakan persamaan Kanai dan intensitas gempabumi menggunakan persamaan Wald. Penelitian ini dilakukan dengan menggunakan 231 data pengukuran mikrotremor di sekitar Kabupaten Bantul yang berasal dari BMKG serta 147 data gempabumi merusak dan terasa dari BMKG. Hasil penelitiaan menunjukkan nilai PGA di Kabupaten Bantul bervariasi dari 57,7-412,7 gal. Zonasi PGA di Kabupaten Bantul dibagi menjadi tiga zona, yaitu zona pertama dengan nilai percepatan 57,7-91 gal, zona kedua dengan nilai percepatan 92-179 gal dan zona ketiga dengan nilai percepatan >180 gal. Sedangkan berdasarkan intensitas gempa bumi, Kabupaten Bantul memiliki potensi kerusakan dalam intensitas V-VII MMI.Kata kunci: Percepatan Tanah Maksimum (PGA), intensitas gempabumi, mikrotremor, periode dominan, Kanai, Wald. ABSTRACTSeismic historical record in Java period of 1981-2014 recorded that the Special Region of Yogyakarta was hit by damaging earthquake 4 times and hundreds of small earthquakes felt. This research was aimed to assess the peak ground acceleration (PGA) zone and the earthquake intensity based on historical data of earthquake occurrence in 1981-2014. Peak Ground Acceleration was calculated using Kanai equation and earthquake intensity using Wald equation. This research was conducted by using 231 microtremor data in Bantul District that derived from BMKG and also 147 data of damaging earthquake and small earthquake felt from BMKG. The result of this study represent peak ground acceleration value in Bantul District which was varied from 57.7-412.7 gal. Peak Ground Acceleration Zonation of Bantul District was diveded by 3 zones; first zone with PGA value 57.7-91 gal, the second zone with PGA value 92-179 gal and the third zone with PGA value higher than 180 gal. While based on earthquake intensity, Bantul District has damage potential of V-VII MMI in intensity scale.

The earthquake that occurred in the Region of Yogyakarta caused by fault activity on the surface, such as Opak-Oyo Fault, Dengkeng Fault, Menoreh Fault and plate tectonic activity in South of Java. Opak-Oyo fault activity reflected from epicenter distribution and earthquake energy. This research aims to analyze the earthquake energy which has epicenter around the Opak-Oyo Fault in spatial and temporal. Based on earthquake catalog from 2008 -2017, there were 66 earthquake event. Epicenter distribution reflected in seismicity map and for the tectonic parameter use least square method. Seismicity map of Opak-Oyo Fault area show that distribution of epicenter in the East and Southeast of fault line with the calculation result of b value by least square method is 0.4. In temporal, there is an increasing trend of events in 2008-2015 and decline trend of earthquake in 2015-2017. Earthquake energy that released in Opak-Oyo Fault area has varies value about 10 5.2 -10 12 Joules. Meanwhile, the energy that associated with the existence of Opak-Oyo Fault Lines has value between 10 5.2 -10 9.6 Joule with 10-20 km of hypocenter. The distribution energy has similar pattern with geological formations in that area.

<p>Ketebalan lapisan sedimen pada suatu wilayah dapat menyebabkan local site effect ketika terjadi gempabumi. Hal ini dikarenakan ketebalan lapisan sedimen berpengaruh terhadap amplifikasi. Kota Pacitan berdasarkan formasi geologi berada pada Formasi Aluvium (<em>Qa</em>) yang didominiasi lapisan sedimen. Penelitian ini bertujuan mengintepretasi ketebalan lapisa sedimen di Kecamatan Pacitan berdasarkan model ground profile <em>Vs </em>hasil akuisisi mikrotremor. Akuisisi dilakukan pada 25 titik di Kecamatan Pacitan menggunakan <em>seimograph portable </em>TDS. Ground profile <em>Vs</em> hasil pemodelan <em>elipticity curve</em>  menunjukkan bahwa nilai <em>Vs</em> bervariasi dari 153.11 m/s  (Formasi Aluvium) sampai 1393.48 m/s (Formasi Batuan Terobosan Andesit). Model ground profile <em>Vs</em> lapisan kedua yang berkorelasi dengan lapisan sedimen berada pada nilai <em>Vs</em>&lt; 750 m/s dengan area di Dataran Aluvial Sungai Grindulu dan Teluk Pacitan. Ketebalan lapisan sedimen hasil analisa ground profile <em>Vs</em>, bervariasi dari 2.59 – 94.37 m. Lapisan sedimen paling tebal terdapat pada Formasi Aluvium (<em>Qa</em>) dengan ketebalan 94.37 m, dan lapisan sedimen paling tipis terdapat pada Formasi Jaten (Tmj) setebal 2.59 m. Lapisan sedimen dengan ketebalan lebih dari 50 m berada di kawasan Kota Pacitan, Teluk Pacitan dan Sungai Grindulu.</p>