Some results of seismic travel-time reflection tomography study

Velocity model is essential for seismic data processing as it plays an important role in migration processes as well as time depth conversion. There are several techniques to reach that goal, among which tomographic inversion is an efficient one. As an upgrade version of handpicked velocity analysis, the tomography technique is based on the reflection ray tracing and conjugate gradient method to estimate an optimum velocity model and can create an initial high quality model for other intensive imaging and modelling module such as reverse-time migration (RTM) and full-waveform inversion (FWI). For the mentioned benefit, we develop a seismic travel-time reflection tomography (SeisT) module to study the accuracy of the approach along with building the technical capability in seismic processing. The accuracy of the module has been tested by both synthetic and real seismic field data; the efficiency and the accuracy of the model have been proven in terms of development method as well as field data application.

Supplemental Material: Early and middle Miocene ice sheet dynamics in the Ross Sea: Results from integrated core-log-seismic interpretation

Additional information regarding methods (Reflection seismic processing, Drill-site measurements, Core-log-seismic correlations, Spatial Velocity calculations, and Reflection Tomography model) and regional stratigraphy descriptions, as well as detailed considerations regarding the opal distribution and depth.

Supplemental Material: Early and middle Miocene ice sheet dynamics in the Ross Sea: Results from integrated core-log-seismic interpretation

Additional information regarding methods (Reflection seismic processing, Drill-site measurements, Core-log-seismic correlations, Spatial Velocity calculations, and Reflection Tomography model) and regional stratigraphy descriptions, as well as detailed considerations regarding the opal distribution and depth.

Reflection tomography by depth warping: A case study across the Java trench

Accurate subsurface velocity models are crucial for geological interpretations based on seismic depth images. Seismic reflection tomography is an effective iterative method to update and refine a preliminary velocity model for depth imaging. Based on residual move-out analysis of reflectors in common image point gathers an update of the velocity is estimated by a ray-based tomography. To stabilize the tomography, several preconditioning strategies exist. Most critical is the estimation of the depth error to account for the residual move-out of the reflector in the common image point gathers. Because the depth errors for many closely spaced image gathers must be picked, manual picking is extremely time-consuming, human biased, and not reproducible. Data-driven picking algorithms based on coherence or semblance analysis are widely used for hyperbolic or linear events. However, for complex-shaped depth events, pure data-driven picking is difficult. To overcome this, the warping method named Non-Rigid Matching is used to estimate a depth error displacement field. Warping is used, e.g., to merge photographic images or to match two seismic images from time-lapse data. By calculating the displacements between an offset to its neighbouring offset in the common image point domain, a locally smooth-shaped displacement field is defined for each data sample. Depending on the complexity of the subsurface, sample tracking through the displacement field along predefined horizons or on a simple regular grid yields discrete depth error values for the tomography. The application to a multi-channel seismic line across the Sunda subduction zone offshore Lombok island, Indonesia, illustrates the approach and documents the advantages of the method to estimate a detailed velocity structure in a complex tectonic regime. By incorporating the warping scheme into the reflection tomography, we demonstrate an increase in the velocity resolution and precision by improving the data-driven accuracy of depth error picks with arbitrary shapes. This approach offers the possibility to use the full capacities of tomography and further leads to more accurate interpretations of complex geological structures.

Supplemental Material: Early and middle Miocene ice sheet dynamics in the Ross Sea: Results from integrated core-log-seismic interpretation

Additional information regarding methods (Reflection seismic processing, Drill-site measurements, Core-log-seismic correlations, Spatial Velocity calculations, and Reflection Tomography model) and regional stratigraphy descriptions, as well as detailed considerations regarding the opal distribution and depth.

Supplemental Material: Early and middle Miocene ice sheet dynamics in the Ross Sea: Results from integrated core-log-seismic interpretation

Additional information regarding methods (Reflection seismic processing, Drill-site measurements, Core-log-seismic correlations, Spatial Velocity calculations, and Reflection Tomography model) and regional stratigraphy descriptions, as well as detailed considerations regarding the opal distribution and depth.

Supplemental Material: Early and middle Miocene ice sheet dynamics in the Ross Sea: Results from integrated core-log-seismic interpretation

Additional information regarding methods (Reflection seismic processing, Drill-site measurements, Core-log-seismic correlations, Spatial Velocity calculations, and Reflection Tomography model) and regional stratigraphy descriptions, as well as detailed considerations regarding the opal distribution and depth.

3-D Architecture and the Upper Miocene-Pliocene Depositional Pattern of the Gulf of İzmir by Reflection Tomography

<p>The ongoing tectonism in the Western Anatolia creates N-S extension and counter-clockwise rotational motion along the right-lateral North Anatolian fault (NAF) and left-lateral East Anatolian Fault (EAF). This continental extension creates predominantly E-W extending onshore grabens rarely NE to SW and NW to SE trending onshore/offshore grabens characterised by the intense seismic activity, high heat flow associated with volcanism, crustal thinning and geothermal systems. Our study area, the gulf of İzmir, has an “L” shape composing of an E-W oriented inner bay from İzmir to Urla and incompatibly NNW-SSE oriented outer bay between offshore Foça and Karaburun. It is located at the intersection of the E-W oriented onshore Gediz Graben and NE-SW oriented onshore Bakırçay graben. Geophysical evidence for fluid discharge and subsurface gas-associated structures such as gas chimneys, pockmarks, mud diapirs and acoustic turbidity zones have been detected in the inner and outer parts of the Gulf of İzmir by the previous studies. For this reason, the Gulf of İzmir and the adjacent onshore grabens are areas of great interest for further study of the region.</p><p>In this study, the 3-D stratigraphic architecture (up to 1.5 km) and the Upper Miocene-Pliocene depositional settings of the Gulf of İzmir reconstructed by reflection tomography for the first time. Three seismic stratigraphic units, labelled SSU1, SSU2 and SSU3 from bottom to top, were identified by their bounding unconformity surfaces (H1-H5). We have subdivided unit SSU1 into three subunits named SSU1c-SSU1a. The acoustic basement associated with SSU3 is likely tied to the Lower-Middle Miocene Yuntdağ Volcanics consisting of tuffs, sandstones, limestones and volcanics. The upper surface of SSU3 (horizon H5) is marked as a major regional unconformity representing a basin-ridge morphology. The first rocks deposited on top of acoustic basement (SSU2) correspond to the sandstones, limestones, volcanics and shales of the Bozköy Formation and the limestones of the Ularca Formation, dating from the Late Miocene to the Pliocene. The top of SSU2 (horizon H4) is interpreted as another unconformity and is correlated with the Pliocene unconformity. Above that, part of the Bayramiç Formation (SSU1c) is dated as Quaternary, consisting of conglomerates at the base overlain by sandstones and shales above. On top of the SSU1c are two further sub-units of the Bayramiç Formation separated by horizons H3 and H2. SSU1b consists of a similar sequence of conglomerates, sandstones and shales; SSU1a consists of Quaternary sandstones. Following the tomographic analysis, the isopach map of the Plio-Quaternary sediment fills was derived from the depth of interpreted horizons calculated using tomographic interval velocities. According to the isopach map of the sedimentary fills, thickness abruptly decreasing from NW to SE. The maximum thickness of total sedimentary succession is ~1400 m in the NW, whereas the thickness decreases through the west, east (up to ~450 m) and the southeastern flank of the basin, reaching ~150 m forming a ridge. A few local lateral velocity variations were identified within the Plio-Quaternary sedimentary succession associated with faults, fluid escape and shallow gas occurrences or a combination of these. </p>