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Marine sand mining activities in Lontar Village have been started legally since 2003 and temporarily halted in 2013. The locals blamed the activities for severe environmental destruction in almost every corner of the village such as low productivity ofaquaculture, coastal erosion, and habitat loss. This paper has an objective to provide preliminary data and analyses for environmental impact assessment of marine sand mining in Serang (Lontar Village). Field investigations were carried out in June 2014 to collect primary data such as bathymetrical data and water quality parameters in the region to understand the environmental conditions after 10 years of marine sand mining activities as well as the characteristicsof local oceanography. Extensive interview with the locals were also conducted to collect information about the socio-economic conditions of the village. Field findings showed that LontarVillage have experienced critical environmental problems such as coastal erosion, high turbidiy and loss of marine lives. Moreover, we also found that the abandoned aquaculture fields have also been converted as sand mining quarries. Recommendations to reduce further environmental damage in Lontar Village are proposed considering both socio-economy and physical aspects.
Keywords:sand mining, Lontar village, environmental damage, erosion
Aktifitas penambangan pasir laut di Kampung Lontar telah dimulai secara legal sejak 2003 dan telah berhenti untuk sementara tahun 2013. Keberatan penduduk setempat terhadap aktifitas penambangan tersebut adalah disebabkan oleh adanya gangguan lingkungan di hampir setiap sudut perkampungan seperti rendahnya produktifitas budidaya perikanan, erosi pantai dan hilangnya. berbagai aneka ragam habitat. Tujuan penelitian ini adalah untuk mendapatkan data awal dan analisis terhadap pengaruh lingkungan akibat aktifitas penambangan pasir laut. Penyelidikan lapangan telah dilaksanakan pada bulan Juni 2014 yaitu untuk mengumpukan data sekunder seperti batimetri dan parameter kualitas air di kawasan tersebut. Penelitian ini adalah untuk mengeahui kondisi lingkungan setelah 10 tahun aktifitas penambangan pasir laut, begitu juga karakteristik oseanografi daerah tersebut. Wawancara intensif dengan penduduk lokal telah dilakukan juga untuk mengumpulkan informasi tentang kondisi sosial ekonomi perkampungan tersebut. Temuan lapangan menunjukkan bahwa perkampungan Lontar mengalami masalah lingkungan yang kritis seperti proses erosi pantai, kekeruhan yang tinggi, dan hilangnya kehidupan laut. Lebih lanjut lagi penelitian ini telah menemukan bahwa sekumpulan ladang budidaya perairan telah beralih menjadi tambang pasir. Saran untuk memperkecil kerusakan lingkungan lebih jauh di Perkampungan Lontar, diusulkan pertimbangan aspek sosial ekonomi dan aspek fisik.
Kata kunci : tambang pasir, Perkampungan Lontar, kerusakan lingkungan, erosi.
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The area from Andaman to northern Sumatran margin is a region where major faults collided that complicates the structural configuration. The origin of structures in the boundary between the accretionary wedge and forearc basin in the northwesternmost segment of the Sunda margin has been a subject of debates. This article reviews several published works on the Andaman – north Sumatran margin to characterize the boundary between forearc basin and accretionary wedge. Complex strain partitioning in this margin is characterized by sliver faults that crossing boundaries between the backarc basin, volcanic arc, forearc basin, and accretionary wedge. The fault zone can be divided into two segments: The West Andaman Fault (WAF) in the north and Simeulue Fault (SiF) in the southern part. A restraining step-over formed in between WAF and SiF. The SiF may extent onshore Simeulue to a strike-slip fault onshore. Strain-partitioning in such an oblique convergent margin appears to have formed a new deformation zone rather than reactivated the major rheological boundary in between the accretionary wedge and forearc basin. The eastern margin of the Andaman-north Sumatra accretionary wedge appears to have form as landward-vergent backthrusts of Diligent Fault (DF) and Nicobar Aceh Fault (NAF) rather than strike-slip faults. This characteristic appears to have formed in the similar way with the compressional structures dominated the eastern margin accretionary wedge of the central and south Sumatra forearc. Keywords: Andaman, North Sumatra, forearc, structure, accretionary wedge, strain partitioningDaerah Andaman - Sumatera bagian utara adalah wilayah di mana patahan-patahan besar saling bertemu dan membuat konfigurasi struktur menjadi rumit. Asal-usul struktur di batas antara prisma akresi dan cekungan busur muka di bagian paling baratlaut dari tepian Sunda telah menjadi topik perdebatan. Artikel ini mengulas beberapa studi yang telah diterbitkan sebelumnya mengenai tepian Andaman - Sumatra bagian utara untuk mengkarakterisasikan batas antara cekungan muka dan prisma akresi. Pemisahan regangan yang kompleks di tepian ini dicirikan oleh sliver fault yang melintasi batas antara cekungan busur belakang, busur vulkanik, cekungan busur muka, dan prisma akresi. Zona sesar tersebut dapat dibagi menjadi dua segmen, yaitu Sesar Andaman Barat (WAF) di utara dan Simeulue Fault (SiF) di bagian selatan. Sebuah restraining step-over terbentuk di antara WAF dan SiF. SiF kemungkinan menerus sampai ke Pulau Simeulue dan menyatu dengan sesar geser. Pemisahan regangan di tepian konvergen yang miring seperti itu tampaknya telah membentuk zona deformasi baru daripada mengaktifkan kembali batas reologi utama di antara prisma akresi dan cekungan busur muka. Batas bagian timur dari prisma akresi di Andaman – Sumatera bagian utara memiliki bentuk sebagai backthrusts berarah darat yaitu Sesar Diligent (DF) dan Sesar Nicobar Aceh (NAF) dan bukan merupakan sesar geser. Karakteristik ini tampaknya terbentuk dengan proses yang mirip dengan struktur-struktur kompresional yang mendominasi bagian timur prisma akresi di daerah Sumatra bagian tengah dan selatan.Kata kunci: Andaman, Sumatera bagian, busur muka, struktur, prisma akresi, pemisahan regangan
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Post tsunami survey of the October 25, 2010, Mentawai tsunami, has been carried out by a collaboration team of Indonesian-German scientists from 20 to 28 November 2010. One activity of the researches were investigation on tsunami deposits along the coast following the event that devastated the islands of Sipora, North Pagai and South Pagai. Sedimentological properties of Mentawai tsunami deposit were explained by this study, from both megascopic and laboratory result. In general, beaches along the study area are underlying by a stretch of reef limestone, sediments mostly composed of white sand while grey sand was found only at Malakopa. Tsunami sediments were taken from 20 locations, start from Betumonga at Sipora Island until Sibaru-baru Island at the southern tip of the study area. The thickness of tsunami deposits are ranged between 1.5 and 22 cm, which are generally composed of fine to coarse sand in irregular boundaries with the underlying soil. Based on grain size analysis, variation of sedimentological properties of tsunami deposits range between phi=-0,5793 and phi=3,3180 or very coarse to very fine sand. Tsunami deposits mostly have multiple layers which described their transport processes, run up at the bottom and back wash at the top. Structural sediments such as graded bedding of fining upward, parallel lamination and soil clast were found. The grain size distribution curves show two types of mode peak, unimodal and multimodal which are indication of different sorting condition representing the source materials. While segment grain size accumulative plot generally shows domination of dilatation and traction transport mechanism rather than suspension. In general, very rare fossils were found from Mentawai tsunami deposit, but those findings gave information on how depth tsunami start to scour the seafloor and transport it landward, such as an abundance of Sponge spicule was found which indicate shallow water environments (20-100 m seafloor depth).
Keywords: 2010 Mentawai tsunami, tsunami deposit, grain size analysis, fossils identification.
Survei pasca-tsunami Mentawai 25 Oktober 2010, telah dilakukan oleh Tim gabungan Indonesia-Jerman pada tanggal 20 - 28 November 2010. Salah satunya adalah melakukan identifikasi endapan tsunami yang ditemukan di sepanjang pantai yang terlanda tsunami di Pulau Sipora, Pagai Utara dan Pagai Selatan. Berdasarkan hasil penelitian baik megaskopik maupun analisis laboratorium, dalam tulisan ini dapat dijelaskan mengenai sifat-sifat sedimentologi dari endapan tsunami Mentawai. Secara umum litologi penyusun pantai di daerah penelitian disusun oleh hamparan batugamping terumbu, sebagian disusun oleh pasir berwarna putih, sedangkan di Malakopa tersusun oleh endapan pasir pantai berwarna abu-abu. Berdasarkan hasil analisis laboratorium, diperoleh variasi sifat sedimentologi, seperti kisaran ukuran butir endapan tsunami antara -0,5793 phi dan 3,3180 phi, yaitu pasir sangat kasar hingga sangat halus. Endapan tsunami umumnya memiliki beberapa lapis yang menunjukkan adanya proses transportasi, seperti saat air naik (run up) di lapisan bagian bawah dan surut di bagian atas, yang ditunjukkan dengan adanya perbedaan ukuran butir. Struktur sedimen ditemukan seperti adanya perubahan besar butir secara berangsur menghalus ke bagian atas, perlapisan sejajar dan fragmen tanah yang terperangkap dalam sedimen. Kurva distribusi ukuran butir memperlihatkan dua jenis model puncak, yaitu unimodal dan multimodal yang memperlihatkan kondisi pemilahan yang berbeda yang menunjukkan kondisi sumber material endapan tsunami, sedangkan grafik akumulasi ukuran butir umumnya memperlihatkan dominasi mekanisme transportasi dilatasi dan traksi daripada suspensi. Secara umum fosil yang terkandung dalam endapan tsunami Mentawai sangat jarang, namun sedikit banyak telah memberikan informasi seberapa dalam gelombang tsunami mulai menggerus lantai samudera dan memindahkannya ke darat, misalnya dengan ditemukannya fosil bentonik Sponge spicule yang melimpah, menunjukkan asal lingkungan laut dangkal dengan kedalaman laut 20-100 m.
Kata kunci: Tsunami Mentawai 2010, endapan tsunami, analisis besar butir, identifikasi fosil.
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The study area is geographically located in the West coast of Belitung island at coordinates 105o48'00" - 106o06' 00" E and 06o46'00" - 06o50' 00" S. The beach and coastal area is influenced by wave energy from the West and North directions The purpose of this study is to analyze the relationship between the zone of sediment accumulation of empirical approaches on oceanography parameter containing rare earth elements. The approach used is to predict the shore wave energy using wave prediction curve deep waters to obtain the energy flux of the wave at each point of reference. Sediments containing rare earth elements tend to lead to the south as a result of the movement of longshore currents. Regional coastal area of the western part of the island of Belitung, especially in the southern part of the estuary of the river Tanjung Pandan is estimated to be a zone of sediment accumulation. The movement of sediment caused by wave energy from the north led to sedimentation evolved significantly in the south which is thought to contain rare earths minerals derived from land. This sedimentation process takes place on a seasonal basis, which allegedly took place in the west. The movement of sediment to the south of the mouth of the Cerucuk River it is predicted that rare earth elements were supplied from these rivers tend to settle in the southern part of the estuary Cerucuk throughout the year.Keywords: accumulation of sediment, longshore currents, rare earth elements offshore Belitung Lokasi daerah penelitian secara geografis terletak di pesisir pantai barat Pulau Belitung pada koordinat 105o48'00" - 106o06'00" BT dan 06o46'00" - 06o50'00"LS. Pesisir pantai termasuk pantai terbuka terhadap pengaruh energi gelombang dari arah barat dan utara. Tujuan dari penelitian ini untuk melakukan analisis hubungan antara zona akumulasi sedimen dari pendekatan empirik parameter osenografi dan kandungan unsur tanah jarang. Pendekatan yang digunakan yaitu dengan memprediksi energi gelombang pantai menggunakan kurva prediksi gelombang perairan dalam untuk memperoleh energi fluks gelombang pada setiap titik referensi. Pengendapan sedimen bermuatan unsur tanah jarang cenderung mengarah ke selatan sebagai akibat dari pergerakan arus sejajar pantai. Daerah kawasan pesisir bagian barat Pulau Belitung terutama di bagian selatan muara sungai Tanjung Pandan diperkirakan menjadi zona akumulasi sedimen. Pergerakan sedimen akibat dari energi gelombang dari arah utara menyebabkan adanya sedimentasi berkembang cukup signifikan di bagian selatan yang diduga bermuatan mineral unsur tanah jarang asal dari darat. Proses sedimentasi ini berlangsung secara musiman, yang kemungkinan berlangsung pada musim barat. Adanya pergerakan sedimen ke arah selatan dari muara Sungai Cerucuk maka diperkirakan unsur tanah jarang yang dipasok dari sungai tersebut cenderung mengendap di bagian selatan dari muara Sungai Cerucuk sepanjang tahun. Kata kunci: akumulasi sedimen, arus sejajar pantai, unsur tanah jarang lepas pantai Belitung
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This paper reports copper, zinc, lead, cadmium, and chromium records of Jakarta Bay sediment since 600 AD and reonstruct environmental changes since that time. Jakarta Bay This study uses samples from a 150 cm long gravity core (TJ-17, 106.902488°E, 5.99381°S) that was acquired from the eastern part of Jakarta Bay in 2010 onboard RV Geomarin I by the Marine Geological Institute. Heavy metal content in Jakarta Bay sediments is used to track environmental changes onland from this site. Heavy metal concentration was analyzed using atomic absorption spectrometry on bulk samples that were taken in 5 cm interval. The results yield background level of Cu at 16 ppm, Zn at 75 ppm, Pb at 20 ppm, Cd at 0.01 – 0.15 ppm, and at Cr 80 ppm. Vertical record of heavy metals show two stages of environmental changes in the region: from 600 AD to 1600 AD and 1800 AD onward. These changes are interpeted as related to land use changes caused by human activity in the West Java region.
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A coastal zone is the interface between the land and water that influenced by both of them. Coastal dynamic is influenced by many factors from land and sea, such as sedimentation and current. In order to support marine facility, Marine Geological Institute of Indonesia (MGI) plan to build a port. The prospective area is behind MGI office at Cirebon. This study use multi temporal remote sensing data in order to observe trend of coastline change around MGI. Based on the interpretation of the data, there are sedimentation around the MGI water and abrasion due to the presence of Kejawanan’s jetty and Kalijaga River. The result also shows that the current in this region is moving from southeast to northwest. The presence of the Kejawanan’s jetty stymies the movement of sediment. The sediment which is normally moving to the north of the jetty is then trapped on the south side of the structure, so that the sediment precipitates in this region and makes it as the active region of sedimentation and accretion. The presence mangrove conduces to support sedimentation speed and accretion at this region, because of his function as the catchment area. Abrasion occurs in the eastern part of MGI office at the Kalijaga river mouth within the bay. The Kalijaga River mouth is predicted to be the primary source of sedimentation in this area. The coastline change caused by sedimentation will be continuing as long as it is supplied by the sediment. The direction of the sedimentation is parallel to the jetty and it forms ellipsoid, with the sedimentation/accretion region is behind MGI office. The abrasion area is found in Kalijaga River mouth and a small area beside Kalijaga River. In order to build a port, we have to consider this sedimentation process. One of the alternatives to build the port is to make a quay pile model which gives way the current to pass through the other side of the port. Another alternative is to build the port as a pond model but it needs accuracy in building the mouth of jetty to minimize the sedimentation process.
Keyword : sedimentation, Cirebon, remote sensing
Pantai/pesisir merupakan wilayah antara daratan dan lautan yang masih dipengaruhi oleh keduanya. Dinamika pantai dipengaruhi oleh faktor-faktor dari daratan dan lautan seperti sedimentasi dan arus. Untuk menunjang “marine facility center†Puslitbang Geologi Kelautan (P3GL) bermaksud untuk membangun pelabuhan. Daerah yang prospektif adalah di belakang kantor P3GL, Cirebon. Studi ini menggunakan data citra satelit multi temporal, yang berguna untuk melihat arah perkembangan dan perubahan garis pantai di belakang kantor P3GL dan sekitarnya. Berdasarkan interpretasi data citra, di daerah studi ditemukan adanya daerah akresi/sedimentasi dan daerah abrasi yang disebabkan oleh adanya dermaga Kejawanan dan adanya sungai Kalijaga. Hasil studi juga menunjukkan arah arus umumnya bergerak dari tenggara menuju barat laut. Keberadaan jetty Kejawanan menyebabkan aliran arus dan sedimen terhenti. Sedimen yang seharusnya bergerak ke arah utama menjadi terhalang dan terjebak di bagian selatan jetty, sehingga mengendap di daerah ini. Keadaan ini menyebabkan daerah ini menjadi daerah sedimentasi yang aktif (akresi). Keberadaan mangrove pada daerah ini juga menambah kecepatan sedimentasi di daerah ini, karena berfungsi sebagai daerah tangkapan sedimen. Abrasi terjadi di sebelah timur P3GL, tepatnya pada daerah lengkungan teluk dan di mulut sungai Kalijaga. Daerah mulut sungai Kalijaga diprediksi sebagai sumber sedimen pada daerah ini. Perubahan garis pantai yang disebabkan oleh sedimentasi akan terus berlangsung di daerah ini, selama adanya pasokan sedimen. Sedimentasi ini akan berlangsung sampai arahnya sejajar dengan jetty Kejawanan dan akan membentuk ellipsoid, dengan daerah sedimentasi berada di sekitar jetty dan belakang P3GL sementara daerah abrasi berada di sungai Kalijaga dan daerah sebelahnya. Karena itu, pembangunan pelabuhan P3GL sebaiknya memperhatikan kondisi ini. Salah satu alternatifnya adalah dengan membuat pelabuhan model tiang pancang yang memungkinkan arus dan sedimen untuk bergerak ke sisi sebelahnya. Alternatif lain adalah dalam bentuk kolam pelabuhan, tetapi harus tepat memperhatikan mulut pelabuhan untuk meminimalkan sedimentasi yang terjadi.
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Bangka Island has primary and secondary tin deposit. However, along the history of tin mining has been done the primary tin deposit domination is less than secondary tin deposit. Secondary tin deposit is formed from Granitic S-type source rock weathering and then transported by gravity. After that, Cassiterite mineral (SnO2) accumulates and forms a placer deposit in the study area. The thickness of sediment cover at Toboali Waters is quite diverse, with a range between 5-20 milliseconds, by knowing the quarter sediment thickness using seismic data interpretation results, is expected to give an idea about tin placer deposit potential in Toboali waters. Based on the Isochron map shows patterns of quaternary sediment thickening to the southwest, south and southeast of Bangka Island.Keywords: Quaternary sediment, placer deposit, isochron map, Toboali WatersPulau Bangka memiliki endapan timah primer dan endapan timah sekunder. Namun, sepanjang sejarah penambangan timah yang telah dilakukan endapan timah primer tidak mendominasi jika dibandingkan dengan endapan timah sekunder. Pembentukan endapan timah sekunder berawal dari pelapukan batuan Granit tipe-S yang kemudian mengalami transportasi akibat adanya gravitasi. Setelah itu, mineral kasiterit (SnO2) terakumulasi dan membentuk endapan plaser di daerah penelitian. Ketebalan sedimen penutup di Perairan Toboali berkisar antara 5-20 milidetik, dengan mengetahui ketebalan sedimen kuarter berdasarkan interpretasi data hasil rekaman seismik diharapkan dapat memberikan gambaran tentang potensi endapan timah placer di Perairan Toboali. Berdasarkan atas peta isokron, memperlihatkan bahwa pola penebalan sedimen kuater ke arah baratdaya, selatan dan tenggara Pulau Bangka.Kata kunci : Sedimen kuarter, endapan placer, peta isokron, Perairan Toboali
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Nongsa Isle belongs to Putri Islands in Batam, is the outermost island that need to be protected either from natural hazards and anthropogenic factor. Therefore, this study was conducted by performing Ground Penetrating Radar analysis, in order to understand the geological condition particularly sedimentology and its process. We used Sirveyor 20 GPR equipment type with MLF antenna frequency 40 Mhz and Radan 5 as processing software, which include time zero correction, spatial filter, deconvolution, migration and adjustment of amplitude and signal gain. Data interpretation was conducted based on radar facies methodology that describes georadar image/radargram. The study result showed differences of sedimentary facies based on three differences of radar facies units, with the first layer (unit 1) is the youngest unit has thicknesses ranging from 3.5 – 5 m that characterized by parallel, strong reflector, high amplitude and continuous reflector configurations, unit 2 from 5 – 11 meter of depth, indicates parallel reflector pattern with medium-high amplitude and continuous, and unit 3 which is the oldest unit with thickness until penetration limit (11 – 20 m), characterized by a configuration of sub parallel – hummocky reflectors that are undulating, low-medium amplitude reflectors. Based on radar facies characteristics such as reflector configuration, reflection amplitude, and reflection continuity, the differencies of depositional facies are changes from fluvial – coastal plain.
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Sea surface salinity (SSS) and precipitation are important climate (paleoclimate) parameters. To obtain long time series data of SSS/precipitation one use coral proxy. In this study, seawater d18O is extracted from d18O content in Bali coral using centering method. The result shows more convincing that d18Obali is influenced by both seawater d18O and sea surface temperature (SST). In the interannual/decadal scale the variation d18Obali clearly shows the variation of seawater d18O, it is supposed that highly variation of precipitation contribute to the seawater d18O variation which mirrored by coral d18Obali.
Keywords: coral d18O, seawater d18O, precipitation, sea surface salinity, sea surface temperature
Salinitas permukaan laut (SSS) dan curah hujan merupakan parameter penting untuk studi iklim maupun paleoiklim (iklim masa lampau). Untuk mendapatkan data dalam urut-urutan waktu (timeseries) yang panjang dari SSS dan curah hujan diperlukan data proksi geokimia dalam koral. Dalam studi ini kandungan d18O dalam air laut dapat di rekonstruksi dari kandungan d18O dalam koral dengan menggunakan metode centering. Hasilnya menunjukkan bahwa d18O dalam koral dipengaruhi oleh kandungan d18O dalam air laut dan SST. Dalam resolusi tahunan dan puluhan tahunan variasi d18Obali dalam koral menunjukkan dengan jelas variasi d18O dalam air laut, hal ini diduga bahwa dalam resolusi tahunan dan puluhan tahunan variasi curah hujan sangat tinggi yang berkontribusi pada tingginya variasi d18Obali dalam air laut sehingga dapat terekam oleh koral.
Kata kunci: d18O koral, d18O air laut, curah hujan, salinitas permukaan laut, suhu permukaan laut.
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The decreasing of fossil fuel reserves in the conventional reservoir has made geologists and geophysicists to explore alternative energy source that could answer energy needs in the future. Therefore the exploration of oil and gas that is still trapped in the source rock (shale) is needed, and one of them still developed in shale gas. The method of Amplitude Versus Offset (AVO) Inversion is used for Lambda-Mu-Rho attributes, that is expected to assess values of physical parameters of shale. Fort Worth Basin is chosen to be a study area because, the Barnett Shale Formation has proven contains of oil and gas. This study using synthetic seismic data, based on geological model and well log data obtained from Vermylen (2012). It is expected from the study of Barnett Shale that related to shale gas development could be applied.
Keyword: Shale gas, Barnett Shale, Fort Worth Basin, AVO Inversion, Lambda-mu-rho attributes
Penurunan cadangan bahan bakar fosil pada reservoar konvensional membuat ahli geologi dan geofisika mengeksplorasi sumber energi alternatif guna menjawab kebutuhan energi di masa depan. Oleh karena itu dibutuhkan eksplorasi minyak dan gas yang masih terperangkap dalam batuan induk (serpih), dan salah satunya yang dikembangkan saat ini adalah “shale gasâ€. Penggunaan metode inversi Amplitudo Versus Offset (AVO) untuk atribut Lambda-Mu-Rho diharapkan dapat menghasilkan nilai-nilai parameter “fisis shaleâ€. Cekungan Fort Worth dipilih sebagai lokasi penelitian ini karena terdapat Formasi “Barnett Shale†yang telah terbukti mengandung minyak dan gas. Penelitian ini menggunakan data seismik sintetik berdasarkan model geologi serta data sumur yang diperoleh dari Vermylen (2012). Diharapkan dari penelitian tentang Barnett Shale yang berkaitan dengan pengembangan shale gas dapat diaplikasikan.
Kata kunci: “Shale gasâ€, “Barnett Shaleâ€, Cekungan Fort Worth, Inversi AVO, atribut Lambda-Mu-Rho
