We performed 3-D seismic tomography using teleseismic arrival time at Southwest Mexico. The Mexican subduction zone results from successive fragmentation events that affected the ancient Farallon plate as various segments of the East Pacific rise approached the paleo-trench off western North America. The complexity in this region is related to two subducting oceanic plates, the Rivera and Cocos plates, that have different ages, compositions, convergence velocities and subduction dip angles. In this study, we compared the 3-D raytracing tomography model with finite frequency tomography model.  Final models show the differences in amplitude and pattern between the raytracing and finite frequency. 3D raytracing models produced sharper images of fast velocity structures in the mantle. The deeper slabs are more coherent and show less broadening with depth than using 1D finite frequency kernels. However, although the finite frequency and 3-D ray tracing models show some differences in amplitude and pattern, the overall agreement of the models supports the interpretation of Yang et al. (2009) that slab rollback is occurring in South Western Mexico.  One possible different interpretation between the raytracing and finite frequency theory results concerns the deep structure of the Rivera slab. The finite frequency models show that the Rivera slab is clearly observable at a depth of about 300km but fades away at greater depths. However, the 3-D ray tracing model shows a clear fast velocity band down to a depth of 400 km and thus our model does not support a slab tear of the Rivera plate above 400 km depth

<p>A novel geotomography technique has been applied in and around Macedonia using selected earthquakes that occurred over a period of 40 years and were recorded on 47 seismograph stations. The aim was to test this new tomography method for the first time in investigation of the crustal shape and structures in that specific tectonic environment with an extensive dataset.</p> <p>A three-dimensional velocity model and many cross-sections of the crust were produced by this methodology and compared with the previous models of Macedonia. They show the potential of the tomography application in revealing geological features on local and regional scale. </p> <p>The new images will contribute towards a better understanding of the seismicity and tectonics in that part of the Balkans and assist in the process of integrated seismic hazard assessment.</p> <p> </p> <p> </p> <p>Keywords: Geotomography, Earthquakes, Seismic Imaging</p>

Daerah Bogor merupakan daerah yang memiliki geomorfologi yang tersusun atas batuan yang bersifat ductile. Suatu bangunan seharusnya didirikan pada suatu lapisan bedrock yang bersifat rigid agar bangunan tersebut dapat berdiri dengan kokoh dan dapat meminimalisir adanya kerusakan bangunan, untuk mengukur dan memodelkan geologi dari bedrock dapat menggunakan metode 2D seismik tomografi dengan irregular mesh pada software GMSH lalu dilakukan inversi tomografi dengan Python. Pemodelan forward dan inversi dilakukan secara berulang hingga diperoleh data traveltime hasil perhitungan berdasarkan model terbaru yang paling sesuai dengan data traveltime observasi. Hasil yang diperoleh adalah pemetaan lapisan bawah permukaan bumi hingga ke bedrock secara detail, dan perhitungan matematis yang cepat. Maka dari itu, dengan menggunakan metode 2D tomografi dengan irregular mesh dapat mengetahui karakteristik lapisan dekat permukaan bumi dengan respon inversi tomografi berupa data kecepatan dan menentukan letak pondasi bangunan.

Often many companies doing seismic reprocessing project with the latest advanced seismic processing technology to handle their seismic problems. This kind of solution might work for some companies but certainly will not for many others. Innovative solutions are required to overcome seismic problem or issue considering time, budget and technical robustness. The objective of this paper is to demonstrate a seismic processing project that was run in a relatively low oil price condition, to handle a low seismic resolution problem in thinly bedded reservoirs. In addition to budget and technical constraints, timing and schedule is also an issue since the updated interpretation is required to be used for updating a static model in less than a 3 months time window. A broadband processing method on 100 km2 post-stack 3D seismic data was applied to enhance frequency content which leads to enhanced seismic resolution to resolve objective reservoirs. This method is considered fast, robust and economical. The procedure would be enhancing the spectrum by designing a unique filter into the dataset after inverse Kirchhoff migration application. After some iterations, forward Kirchhoff migration and multi spatial time-variant filter was applied to generate the desired output. Overall processing time was completed within budget in a one-month period only. As a result, forty percent (40%) increase in dominant frequency was achieved as final deliverables from 25Hz to 35Hz. The original dataset with 25Hz dominant frequency can only resolve reservoirs with thickness greater than 20m. The thickness of individual objective sandstone reservoirs in the study area was ranging from 1.5m to 20m with average thickness around 6-10m. However, stacked reservoir thickness within the same flooding surface interval of the same unit is relatively thicker than 10m. The 35Hz dominant frequency data from broadband processing can resolve reservoir with thickness greater than 14m and better resolve stacked reservoirs even though very thin reservoir below resolution remains unresolved. Broadband seismic technology on post-stack dataset offers a fast, robust and economical solution focused on target which can be duplicated in other area/data to provide successful interpretation projects.