Earthquake Cycle Modelling of Multi-segmented Faults: Dynamic Rupture and Ground Motion Simulation of the 1992 M_w 7.3 Landers Earthquake

We perform earthquake cycle simulations with the goal of studying the characteristics of source scaling relations and strong ground motions in multi-segmented fault ruptures. The 1992 M_w 7.3 Landers earthquake is chosen as a target earthquake to validate our methodology. The model includes the fault geometry for the three-segmented Landers rupture from the SCEC community fault model, extended at both ends to a total length of 200 km, and limited to a depth to 15 km. We assume the faults are governed by rate-and-state (RS) friction, with a heterogeneous, correlated spatial distribution of characteristic weakening distance Dc. Multiple earthquake cycles on this non-planar fault system are modeled with a quasi-dynamic solver based on the boundary element method, substantially accelerated by implementing a hierarchical-matrix method. The resulting seismic ruptures are recomputed using a fully-dynamic solver based on the spectral element method, with the same RS friction law. The simulated earthquakes nucleate on different sections of the fault, and include events similar to the M_w 7.3 Landers earthquake. We obtain slip velocity functions, rupture times and magnitudes that can be compared to seismological observations. The simulated ground motions are validated by comparison of simulated and recorded response spectra

Earthquake Cycle Modelling of Multi-segmented Faults: Dynamic Rupture and Ground Motion Simulation of the 1992 M_w 7.3 Landers Earthquake

We perform earthquake cycle simulations with the goal of studying the characteristics of source scaling relations and strong ground motions in multi-segmented fault ruptures. The 1992 M_w 7.3 Landers earthquake is chosen as a target earthquake to validate our methodology. The model includes the fault geometry for the three-segmented Landers rupture from the SCEC community fault model, extended at both ends to a total length of 200 km, and limited to a depth to 15 km. We assume the faults are governed by rate-and-state (RS) friction, with a heterogeneous, correlated spatial distribution of characteristic weakening distance Dc. Multiple earthquake cycles on this non-planar fault system are modeled with a quasi-dynamic solver based on the boundary element method, substantially accelerated by implementing a hierarchical-matrix method. The resulting seismic ruptures are recomputed using a fully-dynamic solver based on the spectral element method, with the same RS friction law. The simulated earthquakes nucleate on different sections of the fault, and include events similar to the M_w 7.3 Landers earthquake. We obtain slip velocity functions, rupture times and magnitudes that can be compared to seismological observations. The simulated ground motions are validated by comparison of simulated and recorded response spectra

Division of Research and Economic Development Annual Report for FY2005

Annual report for the Division of Research and Economic Development of the University of Rhode Island for the year 2004-2005. Includes statistics of project proposals, expenditures, URI Foundation Awards, previous annual report summaries and awards received by individual academic and administrative departments

Space-Based Remote Sensing of the Earth: A Report to the Congress

The commercialization of the LANDSAT Satellites, remote sensing research and development as applied to the Earth and its atmosphere as studied by NASA and NOAA is presented. Major gaps in the knowledge of the Earth and its atmosphere are identified and a series of space based measurement objectives are derived. The near-term space observations programs of the United States and other countries are detailed. The start is presented of the planning process to develop an integrated national program for research and development in Earth remote sensing for the remainder of this century and the many existing and proposed satellite and sensor systems that the program may include are described

Theory and application of the adjoint method in geodynamics and an extended review of analytical solution methods to the Stokes equation

The initial condition problem with respect to the temperature distribution in the Earth's mantle is Pandora's box of geodynamics. The heat transport inside the Earth follows the principles of advection and conduction. But since conduction is an irreversible process, this mechanism leads to a huge amount of information getting lost over time. Due to this reason, a recovery of a detailed state of the Earth's mantle some million years ago is an intrinsically unsolvable problem. In this work we present a novel mathematical method, the adjoint method in geodynamics, that is not capable of solving but of circumventing the presented initial condition problem by reformulating this task in terms of an optimisation problem. We are aiming at a past state of the Earth's mantle that approaches the current and thus, observable state over time in an optimal way. To this end, huge computational resources are needed since the 'optimal' solution can only be found in an iterative process. In this work, we developed a new general operator formulation in order to determine the adjoint version of the governing equations of mantle flow and applied this method to the high-resolution numerical mantle circulation code TERRA. For our models, we used a global grid spacing of approx. 30 km and more than 80 million mesh elements. We found a reconstruction of the Earth's mantle at 40 Ma that is, with respect to our modelling parameters, consistent with today's observations, gathered from seismic tomography. With this published fundamental work, we are opening the door to a variety of future applications, e.g. a possible incorporation of geological and geodetic data sets as further constraints for the model trajectory over geological time scales. Where high-resolution numerical models and even the implementation of inversion schemes have become feasible over the past decades due to increasing computational resources, in the community there is still a high demand for analytical solution methods. Restricting the physical parameter space in the governing equations, e.g. by only allowing for a radial varying viscosity, it can be shown that in some cases, the resulting simplified equations can even be solved in a (semi-)analytical way. In other words, in these simplified scenarios, no large scale computational resources or even high-performance clusters are needed but the solution for a global flow system can be determined in minutes even on a standard computer. Besides this apparent advantage, analytical and numerical solutions can even go hand-in-hand since numerical computer codes may be tested and benchmarked by means of these manufactured solutions. Here, we spend a large portion of this work with a detailed derivation of these analytical approaches. We basically start from scratch, having the intention to cover all possible traps and pitfalls on the way from the governing equations to their solutions and to provide a service to future scientists that are stuck somewhere in the middle of this road. Besides the derivation, we also present in detail how such an analytical approach can be used as a benchmark for a high-resolution mantle circulation code. We applied this theory to the prototype for a new high-performance mantle convection framework being developed in the Terra-Neo project and published the results along with a small portion of the derived theory. In an additional chapter of this work, we focus on a detailed analysis of the current state of the Earth's gravitational field that is measured in an unimaginably accurate way by the recent satellite missions CHAMP, GRACE and GOCE. The origin of the link of our work to the gravitational field also lies in the analytical solution methods. It can be shown that due to the effect of flow induced dynamic topography, the Earth's gravity field is highly sensitive to the viscosity profile in the Earth's mantle. We show that even without using any other external knowledge or data set, the gravitational field itself restricts the possible choices for the Earth's mantle viscosity to a well-defined parameter space. Furthermore, in the course of these examinations, we found that mantle processes are not capable of explaining the short wavelength signals in the observed gravity field at all, even with the best-fitting viscosity profile. To this end, we developed a simple crustal model that is only based on topographic data (ETOPO) and the principle of isostasy and showed that even with this very basic approach we can explain the majority of short length-scale features in the observed gravity signal. Finally, in combination with a (simple, static and analytic) mantle flow model based on a density field derived from seismic topography and mineralogy, we found a nearly perfect fit of modelled and observed gravitational data throughout all wavelengths under consideration (spherical harmonic degree and order up to l=100)

Structure and tectonics of the crust and Moho discontinuity of the Gloria Fault and Terceira Rift (S. Miguel) along the Nubia-Eurasia plate boundary

The crustal structure of two ~150 km long segments across two main tectonic plate boundaries in the North Atlantic, the Gloria Fault and the Terceira Rift are presented. The Gloria Fault stands as a seismogenic fracture zone that generates high magnitude earthquakes, such as the M8.4 event in 1941. Vp and Vs waves were recorded during an active seismic refraction experiment using 18 Ocean Bottom Stations. The velocity model allows discrimination of five layers (L1 to L5), L1 for sediments, L2 for upper crust, L3 for lower crust, L4 for a layer of unknown origin and L5 for mantle. Poisson coefficient from Vp/Vs ratio allowed estimation of layers’ densities. We speculate on L4 origin and nature from velocities and densities. Two possible models, L4 corresponds to a mixture of gabbro and peridotite or to hydrated mantle (serpentinized mantle). The Terceira Rift seismic refraction line comprehends data from the S. Miguel Island. Velocities of S waves were not recorded. The model is based in Vp only. A five layer model is proposed, L1 for volcano-sedimentary layer, L2 for upper crust, L3 for lower crust and L5 for the mantle. L4 between L3 and L5 has a lensoid shape and its velocities suggest either a cumulate gabbro underplated layer or hydrated mantle. A south dipping extensional shear zone aligned with the Monaco Graben was identified from the brittle upper crust and across the lower crust, L4 and mantle. This shear zone coincides with a cluster of seismicity located to the south of S. Miguel Island. To the north of S. Miguel seismicity is barely inexistent and a 20 km long recent landslide with a toe thrust is clearly imaged, suggesting northward tilting of the island caused by the extensional shear zone, the south flank of the Terceira Rift.German Research Foundation, DFG, grant Hu698/19-

Caribbean plate and geodynamics

Two workshops were held at the LPI in January and February 1978 to discuss possible NASA research topics within the Caribbean area. The meetings explored these scientific topics, then focused on the few most interesting, namely current and past plate motions, earthquake prediction and volcanology.Minutes Compiled at LPI by Thomas R. McGetchin Assisted by Carolyn KohringSummary and Participant List--Letter to Dr. Edward A. Flinn with Recommended Program for NASA/OSTA Geodynamics Program--Agenda, Meeting #1--Agenda, Meeting #2--Summary of Meeting #1--Presentation and Enclosures/Meeting #1--Presentations and Enclosures/Meeting #