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Rhoden A.R.,University of California at Berkeley | Wurman G.,Seismic Inc. | Huff E.M.,University of California at Berkeley | Manga M.,University of California at Berkeley | Hurford T.A.,NASA
Icarus | Year: 2012

We introduce a new mechanical model for producing tidally-driven strike-slip displacement along pre-existing faults on Europa, which we call shell tectonics. This model differs from previous models of strike-slip on icy satellites by incorporating a Coulomb failure criterion, approximating a viscoelastic rheology, determining the slip direction based on the gradient of the tidal shear stress rather than its sign, and quantitatively determining the net offset over many orbits. This model allows us to predict the direction of net displacement along faults and determine relative accumulation rate of displacement. To test the shell tectonics model, we generate global predictions of slip direction and compare them with the observed global pattern of strike-slip displacement on Europa in which left-lateral faults dominate far north of the equator, right-lateral faults dominate in the far south, and near-equatorial regions display a mixture of both types of faults. The shell tectonics model reproduces this global pattern. Incorporating a small obliquity into calculations of tidal stresses, which are used as inputs to the shell tectonics model, can also explain regional differences in strike-slip fault populations. We also discuss implications for fault azimuths, fault depth, and Europa's tectonic history. © 2011 Elsevier Inc..

Takeuchi T.,Tokyo Institute of Technology | Hajjar J.F.,Northeastern University | Matsui R.,Tokyo Institute of Technology | Nishimoto K.,Nippon Steel Engineering Co. | Aiken I.D.,Seismic Inc.
Engineering Structures | Year: 2012

Buckling-Restrained Braces (BRBs) are commonly used as ductile bracing elements in seismic zones. Key limit states governing BRB design include preventing both flexural buckling and local buckling failures. In this study, the authors propose a strategy for the prevention of in-plane local buckling failure of a BRB whose restrainer is composed of a mortar in-filled circular or rectangular steel tube with various mortar thicknesses. Cyclic loading tests on BRBs possessing various mortar restrainers and circular tube thicknesses were carried out to investigate the effect of the mortar and the sectional shape of the restraint tube on the local buckling failure of buckling-restrained braces. © 2012 Elsevier Ltd.

Pekcan G.,University of Nevada, Reno | Itani A.M.,University of Nevada, Reno | Linke C.,Seismic Inc.
Journal of Constructional Steel Research | Year: 2014

An innovative configuration of a Special Truss Girder Frame (TGF) is proposed to facilitate the use of supplemental devices, such as Buckling Restrained Braces (BRBs) and re-centering devices. An energy-based design methodology is adopted such that the devices are designed to provide sufficient energy dissipation capacity with respect to the seismic input energy demand on the structure. The energy based methodology is demonstrated to be accurate by means of a series of nonlinear response history analyses (nRHA). The overall seismic response of the proposed system is evaluated in terms of story displacement, interstory drifts, story shears, overturning moments, and efficiency with respect to the dissipated energy. The proposed configuration and design methodology achieve predictable seismic response with efficient utilization of devices. Furthermore, damage to structural elements is largely mitigated; hence, allowing damage avoidance design of TGF systems, and residual displacements can be mitigated use 013 Elsevier Ltd. ces. © 2013 Elsevier Ltd.

Agency: Department of Defense | Branch: Army | Program: STTR | Phase: Phase I | Award Amount: 99.54K | Year: 2004

The work outlined in this Phase I proposal will advance recently developed SMA beam-column connection concepts toward practical implementation. The work consists of three main tasks: (i) a materials characterization and development program focused on large diameter NiTi martensitic and superelastic bars that will evaluate size effects and thermomechanical processing on stress-strain properties for a range of loading; (ii) designing and analytically investigating the seismic response of a partially-restrained MRF building with SMA beam-column connections, and a building with SMA brace dampers, and (iii) the development of practical design concepts for SMA beam-column connections and preliminary recommendations for the design of structures incorporating SMA connections.

Shen X.,Seismic Inc. | Clapp R.G.,Stanford University
Geophysics | Year: 2015

Three-dimensional waveform inversion is significantly constrained by modern computers' memory size and hard disk access speed. The limitation arises during the gradient calculation steps, in which, in using conventional algorithms, at least one 4D wavefield volume needs to be saved for the calculation. Random boundary conditions (BCs) can be used to avoid the need for saving the 4D wavefield. However, the lower frequency data used in waveform inversion (WI) make the original random boundary designed for reverse time migration (RTM) less effective, leading to undesired artifacts in the gradient. Although increase in boundary size can mitigate this problem, the associated extracomputational cost decreases the computational advantage of the random boundary, particularly in 3D. To maintain the computational advantage of a random boundary region that has a similar size to the one used in RTM and yet still effectively scatter the incidental wavefield into the boundary region, we have proposed a new random boundary design for the low-frequency wave propagation used in WI. The proposed random boundary used larger, irregularly shaped zones of randomized velocities that were effective in introducing incoherency in wavefronts at a large range of wavelengths. The WI using the new random BC gave as good results as the one using absorbing BCs. We have determined the effectiveness of the proposed random boundary design using the finite-difference modeling and synthetic WI examples. © 2015 Society of Exploration Geophysicists.

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