Regional Moment Tensors of the 2009 L'Aquila Earthquake Sequence

Broadband waveform inversion of ground velocities in the 0.02 0.10 Hz frequency band is successfully applied to 181 earthquakes with ML ≥ 3 of the April, 2009, L'Aquila, Italy, earthquake sequence. This was made possible by the development of a new regional crustal velocity model constrained by deep crustal profiles, surfacewave dispersion and teleseismic Pwave receiver functions and tested through waveform fit. Although all earthquakes exhibit normal faulting, with the fault plane dipping southwest at about 55º for the majority of events, a subset of events had much shallower dips. The issue of confidence in the derived parameters was investigated by applying the same inversion procedure by two groups who subjectively selected different traces for inversion. The unexpected difficulty in modeling the regional broadband waveforms of the mainshock as a point source was investigated through an extensive finitefault modeling of broadband velocity and accelerometer data, which placed the location of major moment release updip and about 47 seconds after the initial firstarrival hypocentral parameters

Characteristics of high frequency ground motions in the Maule region (Chile), obtained from aftershocks of the 2010 Mw 8.8 earthquake

The Mw 8.8 Maule earthquake occurred off the coast of central Chile on 2010 February 27, and was followed by thousands of aftershocks. In this study, we modeled 172 aftershocks recorded by more than 100 temporary broadband stations deployed between March 2010 and January 2011. Each of these earthquakes is characterized by a well-determined hypocentral location and well-constrained focal mechanism and moment magnitudes in the range M 3.7 to 6.2. Most of these earthquakes are characterized by shallow, eastward-dipping, thrust-type focal mechanisms consistent with faulting at or near the plate interface, where the Nazca plate is subducting beneath the South America plate at approximately 74 mm/yr. This study provides a unique opportunity to quantify high-frequency earthquake ground motion in a subduction zone due to the quality and quantity of observations in the frequency and distance range of 0.2-30 Hz and 40-500 km, respectively. The analysis was done using a two-step modeling procedure. A regression is performed to characterize source duration and excitation, source-receiver distance dependence, and station site effects. A point source forward model is then constructed in terms of geometrical spreading, duration, site effects and source scaling to match the regression results. This procedure provides the necessary point source parameters for stochastic finite-fault modeling of peak ground motions for future earthquakes in this subduction zone

Numerical Simulation of Nanoscale Double-Gate MOSFETs

The further improvement of nanoscale electron devices requires support by numerical simulations within the design process. After a brief description of our SIMBA 2D/3D-device simulator, the results of the simulation of DG-MOSFETs are represented. Starting from a basic structure with a gate length of 30 nm, the model parameters were calibrated on the basis measured values from the literature. Afterwards variations in of gate length, channel thickness and doping, gate oxide parameters and source/drain doping were made in connection with numerical calculation of the device characteristics. Then a DG-MOSFET with a gate length of 15 nm was optimized. The optimized structure shows suppressed short channel behavior and short switching times of about 0.15 ps.

A regional ground motion excitation/attenuation model for the San Francisco region

By using small-to-moderate-sized earthquakes located within ~200 km of San Francisco, we characterize the scaling of the ground motions for frequencies ranging between 0.25 and 20 Hz, obtaining results for geometric spreading, Q(f), and site parameters using the methods of Mayeda et al. (2005) and Malagnini et al. (2004). The results of the analysis show that, throughout the Bay Area, the average regional attenuation of the ground motion can be modeled with a bilinear geometric spreading function with a 30 km crossover distance, coupled to an anelastic function exp(-pi*f*r/V*Q(f)) , where: Q(f)=180f^0.42. A body-wave geometric spreading, g(r)= r^-1.0, is used at short hypocentral distances (r < 30 km), whereas g(r)= r^-0.6 fits the attenuation of the spectral amplitudes at hypocentral distances beyond the crossover. The frequency-dependent site effects at 12 of the Berkeley Digital Seismic Network (BDSN) stations were evaluated in an absolute sense using coda-derived source spectra. Our results show: i) the absolute site response for frequencies ranging between 0.3 Hz and 2.0 Hz correlate with independent estimates of the local magnitude residuals (dML) for each of the stations; ii) moment-magnitudes (MW) derived from our path and site-corrected spectra are in excellent agreement with those independently derived using full-waveform modeling as well as coda-derived source spectra; iii) we use our weak-motion-based relationships to predict motions region wide for the Loma Prieta earthquake, well above the maximum magnitude spanned by our data set, on a completely different set of stations. Results compare well with measurements taken at specific NEHRP site classes; iv) an empirical, magnitude-dependent scaling was necessary for the Brune stress parameter in order to match the large magnitude spectral accelerations and peak ground velocities with our weak-motion-based model

Aeolian transport layer

We investigate the airborne transport of particles on a granular surface by the saltation mechanism through numerical simulation of particle motion coupled with turbulent flow. We determine the saturated flux $q_{s}$ and show that its behavior is consistent with a classical empirical relation obtained from wind tunnel measurements. Our results also allow to propose a new relation valid for small fluxes, namely, $q_{s}=a(u_{*}-u_{t})^{\alpha}$, where $u_{*}$ and $u_{t}$ are the shear and threshold velocities of the wind, respectively, and the scaling exponent is $\alpha \approx 2$. We obtain an expression for the velocity profile of the wind distorted by the particle motion and present a dynamical scaling relation. We also find a novel expression for the dependence of the height of the saltation layer as function of the wind velocity.Comment: 4 pages, 4 figure

Microscopic Model for Granular Stratification and Segregation

We study segregation and stratification of mixtures of grains differing in size, shape and material properties poured in two-dimensional silos using a microscopic lattice model for surface flows of grains. The model incorporates the dissipation of energy in collisions between rolling and static grains and an energy barrier describing the geometrical asperities of the grains. We study the phase diagram of the different morphologies predicted by the model as a function of the two parameters. We find regions of segregation and stratification, in agreement with experimental finding, as well as a region of total mixing.Comment: 4 pages, 7 figures, http://polymer.bu.edu/~hmakse/Home.htm