Complex Fault System Research Articles

In Search of the Predecessors of the 2011 Van (Turkey) Earthquake

The M w 7.2 earthquake of 23 October 2011 struck an area of Eastern Anatolia with a long historical record and a long earthquake history. The earthquake occurred in a region of rather complex tectonics resulting from the collision of the Arabian and Eurasian continental plates (Tchalenko, 1977; Barka and Reilinger, 1997; McClusky et al. , 2000; Sandvol et al. , 2003; Armijo et al. , 2005). Several studies have recognized the recent and present activity of both the main regional structures and their complex system of conjugate faults (Tchalenko, 1977; Ambraseys, 1989; Berberian, 1997; Bozkurt, 2001; Kocyigit et al. , 2001). The area to the east of the Karliova triple junction and to the north of the Bitlis‐Zagros suture zone is characterized by a north‐south‐compressional tectonic regime, which resulted in a general uplift of the region with the formation of east‐west‐directed thrust and fold belts. A conjugate system of right lateral and left lateral strike‐slip faults paralleling, respectively, the North and East Anatolian faults are also dominant structural elements of the region. The complex compressional structure is also characterized by east‐west‐trending fissures, which resulted in the Plio‐Quaternary activity of the Nemrut, Suphan, and Agri volcanoes, as well as in east‐west‐trending basins of compressional origin such as the Lake Van and Mus basins (Saroglu and Yilmaz, 1986; Bozkurt, 2001). The 23 October 2011 earthquake caused heavy damage to Van and several towns and villages around Lake Van, in the districts of Van and Ercis (Fig. 1). It was followed by several aftershocks and another strong event ( M w 5.7) that occurred on 9 November 2011, causing further damage and casualties. Figure 1. Epicenters of the 23 October ( M w 7.2) and 9 November 2011 ( M w 5.7) earthquakes and damage distribution of …

Small intermediate fault segments can either aid or hinder rupture propagation at stepovers

Large‐scale geometrical complexities along faults are known to be likely endpoints for coseismic rupture, as suggested by analysis of historic ruptures and corroborated by models of rupture on bent or discontinuous faults. However, natural faults also include smaller‐scale complexities. We use the 3D finite element method to model dynamic ruptures on strike‐slip fault stepovers with a smaller intermediate fault between the main strands. We find that such small faults can have a controlling effect on rupture behavior and ground motion intensity and distribution. In particular, the intermediate fault can either aid or prevent rupture propagation across the stepover, depending on its length and basal depth. The results have important implications for hazard assessment of faults with large‐ and small‐scale geometrical complexities, and also suggest that more site‐specific modeling studies may be necessary to develop realistic rupture scenarios for individual complex fault systems.

Assessing the impact of saline intrusion with density dependent flow modelling for the fractured Peninsula Aquifer in Hermanus, South Africa

In the study area of Hermanus, South Africa, the Gateway Wellfield is used to augment municipal water supply. Due to the coastal location, the impact of saline intrusion needs to be considered. The confined Peninsula Aquifer comprises a complex fault system in a fractured rock environment. Analytical equations do not indicate any negative impact of saline intrusion. The impact of different parameters on the interaction between fresh and sea water was tested in a 2D sensitivity analysis. The hydraulic gradient and dispersivity were identified as crucial parameters. In addition, the impact of discrete fractures within a porous medium was tested. Fracture apertures in the likely range of the case study (b < 1 mm) showed a negligible effect. The geology of the Peninsula Aquifer was modelled as an Equivalent Porous Medium (EPM) whereby highly fractured zones around the faults were assigned high hydraulic conductivity. A maximum increase in salinity of 30 mg/l was predicted for the first 20 years of groundwater abstraction. An impact of vertical fractures with b > 1 mm was detected that is hardly predictable. In order to prove the gained conclusions and completely eliminate a harmful impact, further investigations are recommended.

High‐resolution backprojection at regional distance: Application to the HaitiM7.0 earthquake and comparisons with finite source studies

A catastrophicMw7 earthquake ruptured on 12 January 2010 on a complex fault system near Port‐au‐Prince, Haiti. Offshore rupture is suggested by aftershock locations and marine geophysics studies, but its extent remains difficult to define using geodetic and teleseismic observations. Here we perform the multitaper multiple signal classification (MUSIC) analysis, a high‐resolution array technique, at regional distance with recordings from the Venezuela National Seismic Network to resolve high‐frequency (about 0.4 Hz) aspects of the earthquake process. Our results indicate westward rupture with two subevents, roughly 35 km apart. In comparison, a lower‐frequency finite source inversion with fault geometry based on new geologic and aftershock data shows two slip patches with centroids 21 km apart. Apparent source time functions from USArray further constrain the intersubevent time delay, implying a rupture speed of 3.3 km/s. The tips of the slip zones coincide with subevents imaged by backprojections. The different subevent locations found by backprojection and source inversion suggest spatial complementarity between high‐ and low‐frequency source radiation consistent with high‐frequency radiation originating from rupture arrest phases at the edges of main slip areas. The centroid moment tensor (CMT) solution and a geodetic‐only inversion have similar moment, indicating most of the moment released is captured by geodetic observations and no additional rupture is required beyond where it is imaged in our preferred model. Our results demonstrate the contribution of backprojections of regional seismic array data for earthquakes down toM≈ 7, especially when incomplete coverage of seismic and geodetic data implies large uncertainties in source inversions.

The structure of the Sumatran Fault revealed by local seismicity

The combination of the Sunda megathrust and the (strike‐slip) Sumatran Fault (SF) represents a type example of slip‐partitioning. However, superimposed on the SF are geometrical irregularities that disrupt the local strain field. The largest such feature is in central Sumatra where the SF splits into two fault strands up to 35 km apart. A dense local network was installed along a 350 km section around this bifurcation, registering 1016 crustal events between April 2008 and February 2009. 528 of these events, with magnitudes between 1.1 and 6.0, were located using the double‐difference relative location method. These relative hypocentre locations reveal several new features about the crustal structure of the SF. Northwest and southeast of the bifurcation, where the SF has only one fault strand, seismicity is strongly focused below the surface trace, indicating a vertical fault that is seismogenic to ∼15 km depth. By contrast intense seismicity is observed within the bifurcation, displaying streaks in plan and cross‐section that indicate a complex system of faults bisecting the bifurcation. In combination with analysis of topography and focal mechanisms, we propose that the bifurcation is a strike‐slip duplex system with complex faulting between the two main fault branches.

The Porcupine Bank Canyon coral mounds: oceanographic and topographic steering of deep-water carbonate mound development and associated phosphatic deposition

The head of a canyon system extending along the western Porcupine Bank (west of Ireland) and which accommodates a large field of giant carbonate mounds was investigated during two cruises (INSS 2000 and TTR-13). Multibeam and sidescan sonar data (600–1,150 m water depth) suggest that the pre-existing seabed topography acts as a significant factor controlling mound distribution and shape. The mounds are concentrated along the edges of the canyon or are associated with a complex fault system traced around the canyon head, comprising escarpments up to 60 m high and several km long. The sampling for geochemical and petrographic analysis of numerous types of authigenic deposits was guided by sidescan sonar and video recordings. Calcite-cemented biogenic rubble was observed at the top and on the flanks of the carbonate mounds, being associated with both living and dead corals (Lophelia pertusa, Madrepora oculata and occasional Desmophyllum cristagalli). This can plausibly be explained by dissolution of coral debris facilitated by strong currents along the mound tops and flanks. In turn, the dissolved carbon is recycled and precipitated as interstitial micrite. Calcite, dolomite and phosphatic hardgrounds were identified in samples from the escarpment framing the eastern part of the survey area. The laterally extensive phosphatic hardgrounds represent a novel discovery in the region, supplying hard substrata for the establishment of new coral colonies. Based on existing knowledge of regional oceanographic conditions, complemented with new CTD measurements, it is suggested that water column stratification, enhanced bottom currents, and upwelling facilitate the deposition of organic matter, followed by phosphatisation leading to the formation of phosphate-glauconite deposits. The occurrence of strong bottom currents was confirmed by means of video observations combined with acoustic and sampling data, providing circumstantial evidence of fine- to medium-grained sand. Evidently, slope breaks such as escarpments and deep-water canyon headwalls are important structural elements in the development of mature carbonate mounds induced by deep-water coral growth. Stable isotope data show no evidence of methane-derived carbon in the carbonates and lithified sediments of the Porcupine Bank Canyon mounds.

Stress modulation on the San Andreas fault by interseismic fault system interactions

During the interseismic phase of the earthquake cycle, between large earthquakes, stress on faults evolves in response to elastic strain accumulation driven by tectonic plate motions. Because earthquake cycle processes induce non-local stress changes, the interseismic stress accumulation rate on one fault is influenced by the behavior of all nearby faults. Using a geodetically constrained block model, we show that the total interseismic elastic strain field generated by fault interactions within Southern California may increase stressing rates on the Mojave and San Bernardino sections of the San Andreas fault within the Big Bend region by as much as 38% relative to estimates from isolated San Andreas models. Assuming steady fault system behavior since the C.E. 1857 Fort Tejon earthquake, shear stress accumulated on these sections due only to interaction with faults other than the San Andreas reaches 1 MPa, ∼3 times larger than the coseismic and postseismic stress changes induced by recent Southern California earthquakes. Stress increases along Big Bend sections coincide with the greatest earthquake frequency inferred from a 1500-yr-long paleoseismic record and may affect earthquake recurrence intervals within geometrically complex fault systems, including the sections of the San Andreas fault closest to metropolitan Los Angeles.

High-resolution imaging of the deep anisotropic structure of the San Andreas Fault system beneath southern California

SUMMARY Geological and geodetic records show that motion is distributed over a broad and complex system of faults in southern California, with many large earthquakes occurring off the main San Andreas fault. This unusually complex plate boundary geometry is imposed by the big bend of the San Andreas Fault and the dynamics of the underlying lithosphere, but lithosphere rheology and distribution of applied forces are still poorly constrained. Geodynamic modelling is thus very uncertain, and distribution of lithospheric deformations highly controversial. Here, exploiting the property that deformation orients olivine crystals, we show that deep lithospheric deformations can be mapped directly with a new imaging approach of seismic anisotropy, with a resolution fine enough for detailed geodynamic interpretation. This method relies entirely on finite-frequency effects in the splitting of SKS waves. We build an extensive data set of more than 3400 SKS splitting measurements from the analysis of SKS waves recorded by all the broad-band stations in southern California. Resolution tests demonstrate that, using this data set, we are able to resolve anisotropic structures smaller than the size of the first Fresnel zone of SKS waves. The good vertical resolution in our tomographic images results from the short inter-station spacing in southern California. In our 3-D anisotropy model, we find no evidence for localized lithospheric shear deformation beneath the San Andreas Fault. Instead, the lithospheric plate boundary is localized along a broad shear zone beneath the East California Shear Zone. Therefore, surface and deep deformation patterns are poorly correlated and most likely decoupled. Active N–S convergence in the Transverse Ranges results in strongly coherent E–W alignment of olivine fast axes in the shallow lithosphere. At the top of the asthenosphere, the observed low level of anisotropy suggests weak lithospheric basal tractions and thus a strong decoupling between the lithosphere and the asthenosphere.

Tectónica y estratigrafía de la Cuenca Limón Sur

The South Limón Basin is an elongated sedimentary depression located in the back arc region, at the Caribbean side of Costa Rica. This basin has been subjected to several compressional tectonic phases through its geological history. The first compressive tectonic phase is recorded by a series of East to West trending positive structures, as a result of northerly directed stresses that took place in the late Middle Eocene time. The second compressive fault assemblage is related to the subduction of Coco Plate underneath Caribbean Plate, resulting in a cluster of thrust faults as a continuation of the Panamá Deformed Belt. This last tectonic event initiated in the Upper Miocene and has been an active process until the present time. The earthquake of April 22, is thought to be associated to Coco and Caribbean plates collision and to the transmission and liberation of energy along the major East - West trending strike slip fault system that runs through middle Costa Rica from coast to coast. In the Limón area this system joins with the South Limon Thrust Belt. This complex fault system segments Costa Rica into North and South crustal blocks. The South block has been clockwise rotated with respect to the Northern block. The absence of seismicity in the outer part of the South Limón Thrust Belt, support the idea of aseimic lifting probably due to at the front, effect that seems to be an ongoing process since the Upper Miocene until the Present as it is shown in some seismic reflection examples.

Evidence for Vertical Partitioning of Strike-Slip and Compressional Tectonics from Seismicity, Focal Mechanisms, and Stress Drops in the East Los Angeles Basin Area, California

We have synthesized the characteristics of the seismogenic zone in the east Los Angeles basin by analyzing earthquake data recorded during the past 30 years (1981–2010). The seismicity is distributed along the Whittier fault, with the majority of earthquakes located adjacent to the south side, in the depth range from 0 to 9 km, with b value of 1.1±0.05 and mostly normal and strike-slip faulting. Within the depth range of 9–12 km, the seismicity is scattered uniformly across the region, the b value is 1.0±0.05, and all three faulting styles are present. At the deepest depths (12–18 km), seismicity is sparse and primarily limited to a few clusters striking north; these deeper earthquakes primarily have reverse fault motion, and the b value is 0.78±0.04. Inversion of high-quality focal-mechanism data for the orientation of the regional stress field showed that the direction of maximum compressional stress rotates from N12°W at shallow depth to due north at the bottom of the seismogenic zone. Similarly, a depth dependence is observed in stress drops calculated from P-wave source spectra, which indicate stress drop generally increases from ~7 MPa at shallow depth (3 km) to ~53 MPa at the base of the seismogenic zone (17 km). Overall, our results provide new evidence for the vertical partitioning of styles of deformation and state of stress within this complex fault system in the east Los Angeles basin.

A Nitsche-extended finite element method for earthquake rupture on complex fault systems

The extended finite element method (XFEM) provides a natural way to incorporate strong and weak discontinuities into discretizations. It alleviates the need to mesh discontinuities, allowing simulation meshes to be nearly independent of discontinuity geometry. Currently, both quasistatic deformation and dynamic earthquake rupture simulations under standard FEM are limited to simplified fault networks, as generating meshes that both conform with the faults and have appropriate properties for accurate simulation is a difficult problem. In addition, fault geometry is not well known; robustness of solution to fault geometry must be determined. Remeshing with varying geometry would make such tests computationally unfeasible. The XFEM makes a natural choice for discretization in these crustal deformation simulations on complex fault systems. Here, we develop a method based upon the XFEM using Nitsche’s method to apply boundary conditions, enabling the solution of static deformation and dynamic earthquake models. We compare several approaches to calculating and applying frictional tractions. Finally, we demonstrate the method with two problems: an earthquake community dynamic code verification benchmark and a quasistatic problem on a fault system model of southern California.

MPI-OpenMP hybrid simulations using boundary integral equation and finite difference methods for earthquake dynamics and wave propagation: Application to the 2007 Niigata Chuetsu-Oki earthquake (Mw6.6)

Abstract For the past two decades, the combination between the boundary integral equation method (BIEM) and the finite difference method (FDM) has provided a powerful approach for simulating the dynamic rupture process along a complex fault system and the resultant seismic wave radiation and propagation for the purpose of understanding the physics of seismology and the generation of strong ground motion by large earthquakes. In the many-core architecture currently in use, it can be useful to take advantage of hybrid MPI-OpenMP programming. In this study, we are investigating the Mw6.6, 2007 Niigata Chuetsu-Oki, Japan, earthquake. In the BIEM simulation of the dynamic rupture process, MPI-OpenMP hybrid programming is 24 to 38% faster than MPI programming on the same resource using 8 to 16 nodes (with 8 cores). In the FDM simulation on the wave propagation, hybrid programming is 25 to 37% faster. This performance allows us to investigate this earthquake using various parameter settings. First we obtain the frictional parameters based on the proposed kinematic finite source model using BIEM, then model both the spontaneous dynamic rupture propagation and wave radiation by combining BIEM and FDM. It is found that on the given asperities, the peak stress can reach 20 MPa and reduced stress, -20 MPa. Dynamic rupture simulations require a barrier around the southernmost asperity so that this asperity is ruptured in a reverse manner. This effect can be observed very locally in the wave radiation. Furthermore, we observe that the dynamic rupture propagation between two cross-cutting segments generates a more complex wavefield. The change in fault geometry may be dominant over the asperities on a single plane for this earthquake.

Shallow and Deep Structure of a Supradetachment Basin Based on Geological, Conventional Deep Seismic Reflection Sections and Gravity Data in the Buyuk Menderes Graben, Western Anatolia

The Buyuk Menderes Graben is a depression in the Menderes core complex of western Turkey. The region is one of the most rapidly deforming regions of continental crust in the world and has exceptionally high seismic activity. In this study, shallow and deep seismic studies were conducted at the Buyuk Menderes graben. These studies included surface geological mapping and two seismic reflection sections. Detailed modelling was performed with the seismic study. In addition to these, a moving windows power spectrum was applied to the Bouguer gravity profile data of the study area. Since no deep well is available in this area, the geological interpretation of the seismic stratigraphy is based on the correlation with the surface geology, this was combined with the major reflections and the seismic facies observed along the profiles, and, thus, four main seismic units can be distinguished in the basin fill. Structural features of the basin is driven by a complex extensional faults system, consisting of a low-angle, S-dipping Buyuk Menderes detachment and by its synthetic and antithetic splays, bordering the opposite flanks of the basin. As a result of conventional deep seismic reflection sections and gravity data, three layers were defined in the study area. The first layer occurs at a thickness of 6 km, and the second layer is between 13 and 18 km. The third layer is at ~33 km and may also emphasize Moho depth. The Buyuk Menderes graben has three clear reflectors which are base sediments, brittle-ductile transition, Moho and faults that show a half-graben floored by a detachment. The Moho depth is comparable with previous estimates. According to the results obtained, Bouguer gravity and seismic results are very much consistent with each other. It was observed that at the depths determined from seismic and gravity data, the distribution percentage of earthquake focal depths also rises.

Large-scale tracer profiles in a deep claystone formation (Opalinus Clay at Mont Russelin, Switzerland): Implications for solute transport processes and transport properties of the rock

Natural tracers (Cl − and stable water isotopes) in pore water of the Opalinus Clay and adjacent formations were studied in the motorway tunnel at Mont Russelin, Switzerland. The Opalinus Clay occurs in the core of an anticline which is cut by a complex system of thrust faults. Concentration profiles of natural tracers were taken from 17 boreholes along a 363 m long section. Pore waters of drillcore samples were analysed with indirect and direct methods. The Cl − and stable water isotope distribution in the pore water shows a regular and well defined profile, with a conspicuous decrease towards the overlying Dogger limestone aquifer. The highest Cl − values (approximately 23,000 mg/L) are found in the core of the anticline in Liassic claystones underlying the Opalinus Clay. To quantify the large-scale transport properties of the Opalinus Clay formation, a 2D transport model was constructed and used to reproduce the observed concentration profiles. The calculations indicate that the observed tracer distributions are consistent with diffusion as the dominant transport process. Groundwater flow in the overlying Dogger aquifer was initiated about 2–4 Ma ago, which is long after the folding of the Jura Mountains and probably coincides with the exposure of the aquifer to freshwater recharge following continued erosion of the anticline. The calculations suggest that tracer distributions are controlled by 1) the timing of freshwater recharge in the overlying limestone aquifer, 2) the shape of the anticline and 3) the magnitude and the anisotropy ratio of diffusion coefficients.

Structural-stratigraphic control on the Umitaka Spur gas hydrates of Joetsu Basin in the eastern margin of Japan Sea

Integrated geological, geochemical, and geophysical exploration since 2004 has identified massive accumulation of gas hydrate associated with active methane seeps on the Umitaka Spur, located in the Joetsu Basin on the eastern margin of Japan Sea. Umitaka Spur is an asymmetric anticline formed along an incipient subduction zone that extends throughout the western side of the Japanese island-arc system. Seismic surveys recognized chimney structures that seem strongly controlled by a complex anticlinal axial fault system, and exhibit high seismic amplitudes with apparent pull-up structures, probably due to massive and dense accumulation of gas hydrate. Bottom simulating reflectors are widely developed, in particular within gas chimneys and in the gently dipping eastern flank of the anticline, where debris can store gas hydrates that may represent a potential natural gas resource. The axial fault system, the shape of the anticline, and the carrier beds induce thermogenic gas migration to the top of the structure, and supply gas to the gas hydrate stability zone. Gas reaching the seafloor produces strong seepages and giant plumes in the sea water column.

GLOBAL LOW DIMENSIONAL SEISMIC CHAOS IN THE HELLENIC REGION

In this study, we present results concerning seismogenesis in the Hellenic region (land and sea of Greece), applying nonlinear analysis to an earthquake time series. The model of the dripping faucet is used as a physical interpretation of the seismic process and the construction of inter-event seismic time series. Geometrical and dynamical characteristics estimated in the reconstructed state space support the low dimensional, chaotic character of the global seismic process in the Hellenic region. The method of stochastic surrogate data was employed to the exclusion of "pseudo chaos" caused by the nonlinear distortion of a purely stochastic process. These results are in agreement with general theoretical models concerning distributed driven threshold dynamics applied to the case of seismic processes. Moreover, the observed global character of low dimensionality and chaoticity over such a complex system of faults supports the hypothesis that seismogenesis is characterized by spatiotemporal intermittent chaos throughout the Hellenic region.

Dynamic rupture of crosscutting faults: A possible rupture process for the 2007 Mw 6.6 Niigata‐ken Chuetsu‐Oki earthquake

The 2007 Mw 6.6 Niigata‐ken Chuetsu‐Oki earthquake implies a complex fault mechanism. Several surveys suggest the possibility of two main segments crosscutting each other at their center (i.e., a northern segment dipping to the northwest and a southern segment dipping to the southeast). We modeled the dynamic rupture propagation numerically along the inferred segmented fault system using a boundary integral equation method (BIEM). The possibility of rupture transfer is numerically demonstrated, and two rupture modes are described. Simultaneous rupture transfer along the overlapping part is possible only under a high‐stress load; however, this rupture mode yields an excessively high slip value. Otherwise, where regional stress is relatively low but pore pressure is high enough to govern the rupture criterion (described as the low frictional coefficient case in this study), the rupture transfer to the other segment does not occur until rupture terminates on the first segment regardless of the crosscutting distance between the two segments. In this case, at the central crosscutting part, a possible rupture scenario is that ruptures occur sequentially in different directions: first a southbound rupture on the northwest‐dipping segment, then a northbound rupture triggered on the southeast‐dipping segment a few seconds later. The simulated rupture scenario on crosscutting faults can be strongly influenced by a preexisting fault structure determined by Miocene rifting during an opening stage of the Sea of Japan and the subsequent shortening of the crust. Our results point to the importance of investigating earthquake rupture scenarios in complex fault systems based on existing geophysical and geological information and dynamic rupture mechanics.

Boundary integral equations for dynamic rupture propagation on vertical complex fault system in half-space: Theory

The boundary integral equation method (BIEM) is now widely used in numerical studies on earthquake rupture dynamics, and is proved to be a powerful tool to deal with problems on complex fault system. However, since this method heavily lies on the specific forms of Green’s function and only the Green’s function in full-space has a closed analytic expression, it is usually limited to a full-space medium. In this study, as a first step to extend this method to an arbitrary complex fault system in half-space, the boundary integral equations (BIEs) for dynamic strike-slip on vertical complex fault system in half-space are derived based on exact Green’s function for isotropic and homogeneous half-space. Effect of the geometry of the complex fault system are dealt with carefully. Final BIEs is composed of two parts: contribution from full-space, which has been thoroughly investigated by Aochi and his co-workers by using the Green’s function for full-space, and that from free surface, which is studied in detail in this study.

Managing the start-up of a fractured oil reservoir: development of the Clair field, West of Shetland

Abstract The Clair oilfield was discovered in 1977 and began production in 2005. It is a heterogeneous fractured sandstone reservoir with an estimated STOIIP of c . 1.5 billion barrels in the Phase 1 development area. An extended appraisal programme was required to assess reservoir deliverability, which is controlled by the distribution of natural fractures. Development drilling increased the understanding of the fracture system, through acquisition of conventional core, open-hole logging, drilling mud-loss recording, production logging and well test transient analysis. These data revealed a complex fracture system of conductive faults and background joints. Post-production formation pressure measurements showed greater lateral and vertical connectivity than would be expected from matrix and fluid properties alone. However, large pressure differences were encountered close to or across features mappable at a seismic scale. Closed fractures or sealing faults can form baffles between compartments, and conductive faults or fractures allow rapid pressure communication. In some cases the connection path or barrier can be identified with seismically mapped features. When the field was put onto water injection, one year after start-up, a key concern was the degree of imbibition of water from the fractures to the matrix. Despite the observed pressure connectivity, water breakthrough did not take place until 2007. Most producers have completions designed to permit zonal water shut-off. A successful intervention was carried out in early 2008, after a production logging run had demonstrated water entry at the toe of a high-angle well. The crestal Core segment of the development benefits from a permanent 4D seismic array of ocean-bottom cables. In 2007 the first permanent monitor survey was acquired and processing gave indications of a 4D response. These 4D data are improving the dynamic reservoir understanding and providing valuable spatial context to the well results.

Block Modeling with Connected Fault-Network Geometries and a Linear Elastic Coupling Estimator in Spherical Coordinates

Geodetic observations of interseismic deformation provide constraints on the partitioning of fault slip across plate boundary zones, the spatial distribution of both elastic and inelastic strain accumulation, and the nature of the fault system evolution. Here we describe linear block theory, which decomposes surface velocity fields into four components: (1) plate rotations, (2) elastic deformation from faults with kinematically consistent slip rates, (3) elastic deformation from faults with spatially variable coupling, and (4) homogeneous intrablock strain. Elastic deformation rates are computed for each fault segment in a homogeneous elastic half-space using multiple optimal planar Cartesian coordinate systems to minimize areal distortion and triangular dislocation elements to accurately represent complex fault system geometry. Block motions, fault-slip rates, elastic coupling, and internal block strain rates are determined simultaneously using a linear estimator with constraints from both geodetically determined velocity fields and geologic fault-slip rate estimates. We also introduce algorithms for efficiently implementing alternative fault-network geometries to quantify parameter sensitivity to nonlinear perturbations in model geometry.