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The Earth's crust layer and sediment in Western Indonesia has been studied using the inversion of teleseismic receiver function from BMKG’s seismic network. Earthquake events were analyzed in this study with a moment magnitude greater than 6.0 with epicentral distances of 30° to 90°. A total of 60 earthquake events were observed and recorded by 91 stations around the study area. Furthermore, an inversion process was carried out using the initial velocity model from the modification of the AK135f velocity model to obtain the shear wave velocity structure below each stations. The velocity model from the azimuthally stacked vertical receiver function showed that the sediment layer had a relatively medium shear wave velocity value with an average of 2.1 km/s, while the crust layer had 4.60 km/s. The sedimentary layer thickness in this region also varies between 2 km to 10 km. A relatively thick sediment layer of about 8 km to 10 km was observed in two locations, in East Kalimantan associated with the Kutai Basin and Northern part of Sumatera in the North Sumatera Basin, a two major oil producer basinal area in Indonesia. The Moho discontinuity was also found at depths that vary between 16 km to 50 km. In addition, the most shallow Moho depth is 16 km below the North Kalimantan and North part of West Java, while the deeper Moho depth of 50 km is located below East Kalimantan, Central Kalimantan, North Sumatera and South Sumatera.

The existence of seismic wave velocity difference in the Earth crust and mantle creates the possibility to use earthquake data for estimating the crustal thickness utilizing the Ps conversion phase in the boundary. The radial component signal was deconvolved from the vertical component in the frequency domain to estimate receiver function for Indonesia region. We implemented the water level deconvolution techniques with a Gaussian filter of 2.5 Hz to eliminate the high frequency noise in the receiver function. The H-k stacking technique was performed to all receiver functions from each event to predict the crustal thickness and the Vp/Vs ratio below the stations. We analyzed ten azimuthally distributed teleseismic earthquakes recorded by 108 stations of BMKG. The result shows that the crustal thickness in Indonesia varies from 20 to 39.9 km. The western part of Sumatera, northern part of Sulawesi Island, and North Maluku region show generally thinner crust with value about 20 to 25 km. The North Sumatera, Central Java, and East Java show a considerably thicker crust of up to 36 km. Furthermore, our result also reveals a difference of crustal thickness about 5 km with the previous studies.

Indonesia has a high level of seismic vulnerability because located in the junction area of four large plates, namely the Eurasian plate, Indo-Australian plate, Pacific plate, and Philippine Plate, and also the number of active faults that stretch throughout its regions. One of the efforts to mitigate earthquake disasters is to conduct seismic hazard microzonation efforts. The Research and Development Center of BMKG has carried out ongoing research in the field of seismic microzonation to obtain information on the level of seismic hazard in some regions based on microtremor parameter values, including in the Sukabumi (2009), Bantul (2010), Padang (2011), Cilacap (2012), Kulonprogo (2014), Tasikmalaya (2017), Garut (2018) and Pangandaran (2019). This study tries to prototype the seismic microzonation information system in a web-based spatial information system called InaSMIS (Indonesia Seismic Microzonation Information System). InaSIMS contains information about the analysis of microtremor survey results, including the value of the dominant period (T0), Ground Shear Strain (GSS), and USGS Vs30, which states the level of seismic hazard in an area. InaSMIS is still being developed in the research stage and is not yet an operational service for BMKG. In the future, InaSMIS expected to be a source of public information to determine seismic hazards in Indonesian regions.

On May 27, 2006, 05:54 am local time, a moderate crustal earthquake of magnitude Mw 6,3 struck the Yogyakarta province, especially in the Bantul regency in the south part of the province. The earthquake damaged or destroyed more than 400,000 houses and buildings and caused more than 5,700 people killed. Several earthquake stations recorded the ground vibration caused by the mainshock very well, except at the stations closest to the earthquake source, namely YOGI in Gamping, West of Yogyakarta, which experienced saturation due to significant vibration. Therefore, information about the maximum ground acceleration near the source is yet not known. We model the ground vibrations near the earthquake source using a stochastic Green’s Function approach to obtain information about the ground motions’ maximum amplitude. The earthquake source parameters we referred to is the moment tensor solution from the Harvard Moment Tensor. The calculations show that the amplitude is consistent with observations recorded at the BJI Banjarnegara (0.04g) and YOGI Yogyakarta (0.3g).

Earthquake precursors continue to be developed by researchers to try to predict earthquakes, one of which is Radon. The monitoring of radon gas in the ground continues to be carried out in Yogyakarta and its surroundings as one of the earthquake mitigation efforts. This study aims to analyze the variation of radon gas and seismic activity as well as the emergence of local earthquake precursors that occurred in Yogyakarta and its surroundings. Radon gas monitoring is carried out in two locations, namely in the Pundong and Piyungan areas. Earthquake activity was recorded from the BMKG earthquake catalog. The radon anomaly study to determine the existence of earthquake precursors was carried out using the correlation method. Radon gas anomalies are determined when there is an increase in the Radon concentration graph. The results show that an increase in radon gas emissions is correlated with an increase in earthquakes’ frequency. The correlation method’s application indicates the presence of radon gas anomalies as a precursor to earthquakes around the Opak Fault. Further research is needed to see the correlation and consistency of radon gas anomalies with earthquake events around the Opak Fault.

In this study, we used receiver function technique to determine the shear wave velocity profile of the crust and uppermost mantle beneath the eastern part of Indonesia region. We use six BMKG’s permanent stations in the Eastern Indonesia region that recorded about 70 teleseismic events. The receiver function inversion shows a significant variation of sediment thickness layer from about 2 to 4 km in the West Papua region. The crustal thickness variation is estimated at 17 km to 19 beneath Ternate Island and northern Sulawesi, whereas the crustal thickness beneath of the West Papua Region is at 24 km and 37 km. The lithosphere thickness estimate at 40 km to 48 km in Ternate Island and northern Sulawesi while the West Papua Region is around 60 km to 76 km. We found the evidence for a strikingly low-velocity layer starting at about 28 to 30 km depth beneath Ternate islands and northern Sulawesi that may relate to the partial melting zone beneath the active volcano in those areas.

We investigate the sediment and Earth’s crustal structure beneath the East Kalimantan and East Java by modelling the stacked receiver function from six seismic broadband stations belong to the Meteorology, Climatology and Geophysics Agency of Indonesia (BMKG). The calculation of receiver functions from 60 teleseismic earthquake events using iterative time-domain deconvolution method. Inversion result shows a significant variation in the sediment layer thickness from 1 km to 4 km beneath East Java. It is correlated with the South East Java basinal area (station KRK) and the North East Java Basin (station GRJI and BWJI). The sediment layer of about 5 to 10 km beneath East Kalimantan is associated with the Kutai Basin (station SGKI, SMKI, and BKB). Average Sediment layer shear velocity (Vs) beneath all station is observed to be less than 2.31 km/s. Crustal thickness beneath East Java varies between 20 to 40 km and 34 to 50 km beneath East Kalimantan, with average crustal shear wave velocity, Vs 4.60 km/s.

We have conducted geoelectric resistivity and shear wave velocity (Vs30) study to identify the landslide potential hazard, around Geophysics Station Lembang, Bandung (107,617° E and 6,825° S). The the geoelectric analysis using Dipole-Dipole resitivity configuration, while shear wave velocity analysis performed using the Multichannel Analysis of Surface Wave (MASW). The study results indicate that the assumed soil or clay depth from the electrical resistivity observation was in accordance with the confirmed soil or clay depth by the MASW investigation. Based on these conditions, indicate the high potential of landsliding in this area, landslide potential supported by high slope angle in this area.

We present a magnitude of completeness (Mc) quantification based on BMKG improved earthquake catalog which generated from Ina-TEWS seismograph network. The Mc quantification can help us determine the lowest magnitude which can be recorded perfectly as a function of space and time. We use the BMKG improved earthquake catalog from 2008 to 2016 which has been converted to moment magnitude (Mw) and declustered. The value of Mc is computed by determining the initial point of deviation patterns in Frequency Magnitude Distribution (FMD) chart following the Gutenberg-Richter equations. In the next step, we calculate the temporal variation of Mc and b-value using maximum likelihood method annually. We found that the Mc value is decreasing and produced a varying b-value. It indicates that the development of seismograph network from 2008 to 2016 can affect the value of Mc although it is not significant. We analyze temporal variation of Mc value, and correlate it with the spatial distribution of seismograph in Indonesia. The spatial distribution of seismograph installation shows that the western part of Indonesia has more dense seismograph compared to the eastern region. However, the eastern part of Indonesia has a high level of seismicity compared to the western region. Based upon the results, additional seismograph installation in the eastern part of Indonesia should be taken into consideration.

Salah satu metode geofisika yang dapat mengetahui profil penampang bawah permukaan untuk mengetahui potensi likuifaksi adalah metode resistivitas geolistrik. Penelitian ini bertujuan untuk mengetahui gambaran resistivitas lapisan tanah yang memiliki potensi likuifaksi di daerah Cilacap. Penelitian ini menggunakan 33 titik pengukuran resistivitas geolistrik dimana hasil analisis resistivitas ditampilkan dalam bentuk penampang melintang lapisan bawah permukaan. Analisis potensi likuifaksi berdasarkan resistivitas batuan dilakukan dengan mempertimbangkan informasi tingkat kepadatan relatif dan uji kekuatan (N-SPT) serta karakteristik batuan lepas. Nilai resistivitas di daerah penelitian berkisar antara 0.09 – 585Wm. Berdasarkan informasi geologi maka nilai resistivitas yang terukur di daerah penelitian menunjukkan litologi aluvium berupa pasir, kerikil dan kerakal (100 – 585 Wm), aluvium berupa lempung dan lanau (14 – 85 Wm), akuifer air (1.6 – 15 Wm), lapisan lempung (0.09 – 1.5 Wm), napal tufaan (6 – 95 Wm) serta pasir tufaan sisipan batupasir (1.3 – 8 Wm), yang merupakan satuan batuan dari Formasi Halang. Daerah Cilacap mempunyai potensi likufaksi yang relatif tinggi dikarenakan memiliki karakteristik fisik yang tersusun oleh endapan Kuarter dengan tingkat kepadatan dan sifat keteknikan tanah bawah permukaan dicirikan material sangat lepas hingga agak padat, memiliki muka air tanah yang dangkal, secara fisiografi berhadapan langsung dengan laut yang menyebabkan sedimen penyusunnya jenuh air, dan berada di lokasi yang rawan gempabumi besar. One of the geophysical methods to determine subsurface cross-section profiles to determine the liquefaction potential is the geoelectric resistivity method. This study aims to describe the resistivity layer of soil liquefaction potential in Cilacap. This study uses 33 measurement points where the geoelectric resistivity analysis results are displayed in the subsurface cross-section profile. Analysis of liquefaction potency based on the resistivity of rock performed by considering relative density level information and strength test (N-SPT) and unconsolidated rock characteristics. Resistivity value in the study area ranged from 0.09 - 585 Wm. Based on geological information, the resistivity values measured in research area show lithology of alluvium i.e. sand, granule and pebble (100-585 Wm), alluvium i.e. clay and silt (14-85 Wm), aquifers (1.6 - 15 Wm), layer of clay (0.09 - 1.5 Wm), tuffaceous marl (6-95 Wm), inserted tuffaceous sandstone (1.3 - 8 Wm), all of which are Halang formation lithology. Cilacap area has the relative high liquefaction potential due to the physical characteristics composed by Quaternary sediment with density and subsurface soil engineering that very loose until rather dense, has a shallow groundwater-surface, in the physiographic located near the coast which water-saturated sediments constituent, and located in a great earthquake-prone location.

Cilacap merupakan daerah yang sering merasakan dampak guncangan gempabumi. Populasi penduduk yang besar dan keberadaan obyek penting pemerintah menjadi suatu pertimbangan diperlukannya kajian efek guncangan gempabumi. Tujuan penelitian ini adalah untuk memetakan daerah yang memiliki potensi mengalami kerusakan akibat guncangan gempabumi berdasarkan jenis tanah hasil analisis kecepatan gelombang geser (Vs) sebagai salah satu upaya mitigasi bencana gempabumi. Nilai Vs didapatkan dari pengukuran Multichannel Analysis of Surface Wave ( MASW ) pada 14 lokasi dan pengolahan menggunakan perangkat lunak WinMASW untuk mendapatkan profil Vs 1D. Selanjutnya dibuat sayatan selatan – utara dan barat daya–timur laut untuk mendapatkan gambaran Vs secara 2D. Hasil penelitian menunjukkan bahwa daerah penelitian memiliki nilai Vs rata-rata (0-30 m) antara 153 m/s – 355 m/s. Berdasarkan sayatan 2D tersusun oleh jenis tanah lunak (Vs ≤ 175 m/s), jenis tanah sedang (175 < Vs ≤ 350m/s), dan jenis tanah keras (Vs ≥ 350 m/s), dengan dominasi utama adalah tanah sedang dengan endapan sedimen yang cukup tebal. Hal ini menyebabkan daerah penelitian terutama di bagian selatan, tengah, dan barat berpeluang besar mengalami guncangan yang lebih besar ketika terjadi gempabumi, sehingga berpotensi mengalami kerusakan yang lebih besar. Sedangkan daerah yang relatif aman untuk pengembangan wilayah berada di sisi utara dan timur daerah penelitian karena tersusun atas endapan sedimen tipis dan tanah yang keras. Cilacap is an area that often suffers earthquake shocks impact. A large population and the existence of important government object becomes a consideration for a study related to earthquake shocks effect. This study aims to map areas that have potential damages due to earthquake, based on soil type from shear wave velocity (Vs) analysis, as an effort to earthquake disaster mitigation. Vs obtained from Multichannel Analysis of Surface Wave(MASW) at 14 locations and processed using WinMASW software to obtain a 1D velocity profile. Further, a 2D incision was made for south-north (A-A') and southwest-northeast (B-B') to obtain a 2D Vs profile. The results showed an average value of Vs (0-30m) between 153 - 355 m/s. Based on 2D incision result, the soil is arranged in layers by soft soil (Vs ≤ 175 m/s), medium soil (175

Gempabumi bermagnitudo 4,8 SR mengguncang Bogor dan sekitarnya pada Minggu 9 September 2012. Gempabumi ini berpusat di 6.70 o LS dan 106,64 o BT, dengan kedalaman 10 km. Akibatnya lebih dari 500 rumah dilaporkan mengalami kerusakan yang tersebar di Kabupaten Bogor dan Sukabumi. Kerusakan terparah terjadi di desa Cibunian dan Purwabakti, Kecamatan Pamijahan, Bogor. Penelitian ini bertujuan untuk mengetahui efek tapak lokal di daerah kerusakan akibat gempabumi Bogor 9 September 2012 berdasarkan pengukuran mikrotremor. Pengambilan data mikrotremor pada penelitian ini dilakukan di 13 titik di desa Cibunian dan Purwabakti yang merupakan daerah yang mengalami kerusakan paling parah akibat gempabumi Bogor. Pengukuran dilakukan dengan menggunakan portable digital seismograph 3 komponen dengan durasi pengukuran selama 30 menit dan frekuensi sampling 100 Hz. Pengolahan data menggunakan metode HVSR ( Horizontal to Vertical Spectrum Ratio ) dengan software G eopsy . Hasil Penelitian menunjukkan bahwa nilai frekuensi predominan ( fo ) di daerah penelitian berkisar antara 1,0 – 7,2 Hz, sementara itu variasi faktor amplifikasi ( A ) antara 1,0 – 4,1 dimana sebagian besar nilai < 3. Variasi nilai indeks kerentanan seismik ( Kg ) berkisar antara 0,4 – 8,9 yang menggambarkan bahwa daerah penelitian mempunyai tingkat kerentanan yang relatif rendah apabila terjadi gempabumi. Sedangkan nilai ground shear strain yang terhitung berkisar 2x10 -4 – 3x10 -3 , yang mengindikasikan goncangan yang tidak terlalu besar di daerah penelitian. Hal ini menunjukkan bahwa kerusakan parah yang terjadi di beberapa lokasi, bukan karena fenomena efek tapak lokal, melainkan lebih dominan disebabkan oleh konstruksi dan kualitas bangunan yang kurang baik. On September 9, 2012, an M4.8 earthquake struck the Bogor region, in which the epicenter was determined by BMKG at 6.70°S and 106.64°E, with a depth 10 km. The earthquake affected more than 500 building in Bogor and Sukabumi were damage. The worst damage occurred in Cibunian and Purwabakti in Pamijahan District, Bogor. This research aims to determine the local site effect due to the Bogor earthquake based on microtremor measurements. Microtremor measurements conducted at 13 points in Cibunian and Purwabakti, using a digital portable seismograph 3 components with 30 minutes duration measurement and 100 Hz sampling frequency. Data processing use HVSR (Horizontal to Vertical Spectrum Ratio) method on Geopsy software. The results show that predominant frequency (fo) ranged from 1.0 to 7.2 Hz, while the variation of amplification factor (A) between 1.0 to 4.1 with most values

A geophysic survey is performed to detect subsurface structure under STMKG Campus in Pondok Betung, South Tangerang, Indonesia, using seismic refraction method. The survey used PASI 16S24-U24. The waveform data is acquired from 3 different tracks on the research location with a close range from each track. On each track we expanded 24 geofons with spacing between receiver 2 meters and the total length of each track about 48 meters. The waveform data analysed using 2 different ways. First, used a seismic refractionapplication WINSISIM 12 and second, used a Hagiwara Method. From both analysis, we known the velocity of P-wave in the first and second layer and the thickness of the first layer. From the velocity and the thickness informations we made 2-D vertical subsurface profiles. In this research, we only detect 2 layers in each tracks. The P-wave velocity of first layer is about 200-500 m/s with the thickness of this layer about 3-6 m/s. The P-wave velocity of second layer is about 400-900 m/s. From the P-wave velocity data we interpreted that both layer consisted by similar materials such as top soil, soil, sand, unsaturated gravel, alluvium and clay. But, the P-wave velocity difference between those 2 layers assumed happening because the first layer is soil embankment layer, having younger age than the layer below.

Monitoring parameter geo-atmosferik dan geokimia sebagai perpaduan dari monitoring emisi gas radon, suhu udara permukaan, suhu dan kelembaban tanah dilakukan di Stasiun Observatori Geofisika Pelabuhan Ratu, Sukabumi, Jawa Barat untuk mengetahui hubungannya dengan aktivitas gempabumi. Penelitian di Indonesia mengenai hubungan parameter geo-atmosferik dan geokimia dengan prekursor gempabumi baru pertama kali dilakukan oleh Pusat Penelitian dan Pengembangan Badan Meteorologi Klimatologi dan Geofisika (Puslitbang BMKG). Monitoring gas radon, suhu, dan kelembaban tanah dilakukan menggunakan sistem monitoring radon RAD7 dengan sensor soil gas probe yang ditanam pada kedalaman 1,2 meter. Data pengamatan suhu permukaan adalah suhu maksimum dan minimum yang tercatat menggunakan termometer air raksa. Anomali radon, suhu, dan kelembaban dikorelasikan dengan kejadian gempabumi yang memenuhi radius zona manifestasi prekursor berdasarkan penelitian Dobrovolsky. Hasil analisis parameter geo-atmosferik menunjukkan adanya penurunan sebesar 5,3°-13° yang diikuti kenaikan sebesar 6°-8,2° pada nilai Tmax-Tmin suhu permukaan. Sementara untuk analisis geokimia menunjukkan adanya kenaikan gas radon sebesar 1,5-60 kali dari nilai normalnya, kenaikan kelembaban sebesar 6%-21%, dan kenaikan suhu tanah 1,5°-3,2° yang diikuti penurunan sebesar 1,5°-4°. Anomali geo-atmosferik dan geokimia yang diduga sebagai prekursor gempabumi terdeteksi 3-30 hari sebelum gempabumi sehingga parameter ini termasuk dalam prekursor jangka pendek yang berhubungan dengan proses deformasi di wilayah pengamatan sebelum gempabumi. Monitoring of geo-atmospheric and geochemical parameters, as a combination monitoring of radon emission, surface air temperature, and soil temperature and humidity, located in Geophysical Observatory Station Pelabuhan Ratu, Sukabumi, West Java, to determine its relation with the earthquake. In Indonesia, it was the first research of earthquake precursors using these methods, conducted by Research and Development Center, Indonesian Agency of Meteorology Climatology and Geophysics. Monitoring of radon, soil temperature and humidity using RAD7 radon monitoring system where probes sensor are placed at 1.2 meters below land surface. The maximum and minimum air temperature recorded by a mercury thermometer. The anomalies of radon, temperature, and humidity are correlated with the occurrence of earthquakes within a radius of precursor manifestation zone, refer to Dobrovolsky's research. The results of analysis show a decrease of 5.3°-13° which followed by an increase of 6°-8.2° on the surface temperature; an increase of radon gas at 1.5-60 times of the normal value, the increase of humidity ranged on 6% -21%, and the soil temperature rise of 1.5°-3.2° followed by a decrease of 1.5°-4°. Geo-atmospheric and geochemical anomalies indicated as precursors detected 3-30 days before the earthquake and categorized as short-term precursors that associated with the deformation process in the observation region before the earthquake.

Telah dilakukan penelitian menggunakan metode seismik refraksi di daerah Sumbawa yang bertujuan untuk menentukan tingkat kekerasan batuan. Pengambilan data lapangan dalam bentuk lintasan dan dibagi tiga bagian, yaitu menggunakan end-off spread di kedua ujung dan mid-spread. Tahapan pengolahan data diawali dengan melengkapi informasi posisi dari masing-masing geophone dan sumber seismiknya dengan mengedit geometri, sehingga dapat dikenali oleh komputer sebagai satu kesatuan data base. Untuk menghilangkan noise yang menenggelamkan sinyal firstbreak , dilakukan proses BPFB ( Band Pass Filter Butterworth ) sebesar 10-100 Hz. Proses inversi yang digunakan adalah refraction tomography , dengan pendekatan non linier least square inversion dan perhitungan pemodelan maju untuk menghitung nilai Vp menggunakan forward refraction raytracing . Penentuan densitas batuan menggunakan rumus empiris Gardner's relationship . Hasil interpretasi data menunjukkan empat lapisan batuan dengan kecepatan rambat gelombang P adalah 200-1800 m/sec dan densitasnya 1.17-2.05 gr/cc. Pengelompokan lapisan berdasarkan kecepatan rambat gelombang P adalah lapisan pertama (200-700 m/sec), lapisan kedua (700-1100 m/sec), lapisan ketiga (1100-1700 m/sec) dan lapisan keempat (>1700 m/sec). Litologi batuan bawah permukaan terdiri dari soil (1.17-1.59 g/cc), granodiorit lapuk kuat (1.59-1.78 gr/cc), granodiorit lapuk lemah (1.78-1.99 gr/cc) dan granodiorit segar (>1.99 gr/cc). Batuan keras terdapat dari permukaan hingga kedalaman 30 meter. Seismic refraction research have been done in Sumbawa to determine the level of rocks density. Field data acquisition in lines and are divided into three parts that are end-off spreads at both ends and mid-spreads. The first step of the processing was to identified positions of each geophone and its shot by editing the geometry, so it can be recognized by computer as a single unified database. Bandpass Filter Butterworth process at 10-100 Hz has been done to eliminate noise that drowned the firstbreak signal. Inversion process using the refraction tomography with non-linear least squares inversion approach and the forward modeling for calculate Vp value using forward refraction raytracing. While the rock density determination used empirical formula from Gardner's relationship. Results of the interpretation shows four layers of rock with the P-wave propagation velocity are 200-1800 m/sec and density are 1.17-2.05 g/cc. Grouping layers based on the P-wave propagation velocity are the first layer (200-700 m/sec), second layer (700-1100 m/sec), third layer (1100-1700 m/sec) and fourth layer (>1700 m/sec). Sub-surface lithology consists of soil (1.17-1.59 g/cc), strong weathered layer of granodiorite (1.59-1.78 g/cc), weak weathered layer of granodiorite (1.78-1.99 g/cc) and fresh granodiorite (>1.99 g/cc). Hard rock layer found from surface to 30 meters depth.

Salah satu metode untuk mendapatkan informasi mengenai struktur di bawah permukaan bumi adalah receiver function. Konsep dasar metode receiver function ini adalah pendekatan kedalaman kerak bumi dengan menggunakan informasi waktu tunda dari fase gelombang Ps yang merupakan konversi dari pantulan gelombang P menjadi gelombang S pada batas mantel-kerak bumi. Akurasi ditingkatkan dengan menggunakan bantuan dari waktu tiba fase-fase gelombang lain yang tiba setelahnya, yaitu fase gelombang PpPs dan PpSs+PsPs. Program diuji menggunakan dua buah model kecepatan 4 lapis dengan variasi kecepatan yang besar berada pada kedalaman masing-masing 32 km dan 38 km. Dari hasil perhitungan dengan menggunakan metode stacking H-k ini diperoleh kedalaman interface kerak sebesar 32 km dan 38 km yang bersesuaian dengan model yang dibuat. Perhitungan dengan H dan k masing-masing sebanyak 301 sample (total 301 × 301 kali perhitungan maju receiver function) diperlukan waktu selama 20 detik pada komputer dengan processor Intel Dual Core dan memori sebesar 2 GHz. One of methods to obtain information about structure beneath the earth's surface is receiver function. The basic concept of receiver function method is to estimate of the Earth's crust depth using phase delay information from Ps wave which is a conversion from P wave reflection to S wave at the earth’s crust-mantle boundary. The accuracy of the calculated depth was enhanced by using additional phases that arrived after that, i.e. PpPs and PpSs + PSPs. The program was examined using two models, each have a four-layer velocity models with large velocity contrast at 32 km and 38 km of depth. We obtained that the depth of crust interface are about 32 km and 38 km. These depths correspond to the velocity model. It takes 20 seconds on a computer with an Intel Dual Core with memory of 2 GHz to calculate the model with 301 x 301 samples of H and k

Telah dilakukan pengukuran mikrotremor di 71 titik di Sumbawa. Daerah penelitian dibatasi pada koordinat 117.21250°-117.22750°BT dan 8.7850°-8.8150°LS. Penelitian ini bertujuan untuk mengetahui karakteristik dinamis kondisi geologi lokal diantaranya frekuensi resonansi (fo) dan indeks kerentanan seismik (Kg) serta nilai percepatan getaran tanah (PGA) menurut formulasi Kannai. Pengukuran mikrotremor dilakukan pada masing-masing titik pengukuran selama 30 menit dengan menggunakan Digital Portable Seismograph. Dari analisa data diperoleh nilai frekuensi resonansi (fo) yang relatif tinggi berkisar antara 24,4 hingga 48,14 Hz dan nilai indeks kerentanan seismik (Kg) yang relatif rendah berkisar antara 0,1 hingga 4,8. Hal ini berkaitan erat dengan kondisi geologi lokal berupa batuan yang masif, sehingga daerah dengan frekuensi resonansi tinggi dan indeks kerentanan yang rendah relatif stabil secara seismik. Nilai PGA di daerah kajian berkisar antara 0,25 hingga 0,36 g. Nilai PGA di daerah kajian menunjukkan variasi yang tidak terlalu mencolok yang menunjukkan nilai PGA lebih banyak dipengaruhi oleh input nilai periode dominan di daerah kajian. Microtremor measurements have been done at 71 points in Sumbawa. The research area is restricted to the coordinate 117.22750°-117.21250°E and 8.7850°-8.8150°S. This study aims to determine the local dynamic characteristics including the resonance frequency (fo), seismic vulnerability index (Kg) and peak ground acceleration (PGA) according to Kannai formulation. Microtremor measurements carried out at each point for 30 minutes using Digital Portable Seismograph. From the data analysis obtained the resonance frequency (fo) value are relatively high ranging from 24.4 to 48.14 Hz and seismic vulnerability index (Kg) values are relatively low ranging from 0.1 to 4.8. It is closely related to local geological conditions in the form of a massive rock, so that area with a high resonance frequency and relatively low vulnerability index is seismically stable. PGA values in the study area ranged from 0.25 to 0.36 g. PGA values showed a less variations that indicate PGA value is more influenced by the input value of the dominant period in the study area.