Long-Period Building Response to Earthquakes in the San Francisco Bay Area

This article reports a study of modeled, long-period building responses to ground-motion simulations of earthquakes in the San Francisco Bay Area. The earthquakes include the 1989 magnitude 6.9 Loma Prieta earthquake, a magnitude 7.8 simulation of the 1906 San Francisco earthquake, and two hypothetical magnitude 7.8 northern San Andreas fault earthquakes with hypocenters north and south of San Francisco. We use the simulated ground motions to excite nonlinear models of 20-story, steel, welded moment-resisting frame (MRF) buildings. We consider MRF buildings designed with two different strengths and modeled with either ductile or brittle welds. Using peak interstory drift ratio (IDR) as a performance measure, the stiffer, higher strength building models outperform the equivalent more flexible, lower strength designs. The hypothetical magnitude 7.8 earthquake with hypocenter north of San Francisco produces the most severe ground motions. In this simulation, the responses of the more flexible, lower strength building model with brittle welds exceed an IDR of 2.5% (that is, threaten life safety) on 54% of the urban area, compared to 4.6% of the urban area for the stiffer, higher strength building with ductile welds. We also use the simulated ground motions to predict the maximum isolator displacement of base-isolated buildings with linear, single-degree-of-freedom (SDOF) models. For two existing 3-sec isolator systems near San Francisco, the design maximum displacement is 0.5 m, and our simulations predict isolator displacements for this type of system in excess of 0.5 m in many urban areas. This article demonstrates that a large, 1906-like earthquake could cause significant damage to long-period buildings in the San Francisco Bay Area

Adverse drug reactions from psychotropic medicines in the paediatric population: analysis of reports to the Danish Medicines Agency over a decade

<p>Abstract</p> <p>Background</p> <p>The prescribing of psychotropic medicines for the paediatric population is rapidly increasing. In attempts to curb the use of psychotropic medicine in the paediatric population, regulatory authorities have issued various warnings about risks associated with use of these products in childhood. Little evidence has been reported about the adverse drug reactions (ADRs) of these medicines in practice. As spontaneous reports are the main source for information about previously unknown ADRs, we analysed data submitted to a national ADR database. The objective was to characterise ADRs reported for psychotropic medicines in the Danish paediatric population over a decade.</p> <p>Findings</p> <p>All spontaneous ADR reports from 1998 to 2007 for children from birth to 17 years of age were included. The unit of analysis was one ADR. We analysed the distribution of ADRs per year, seriousness, age and gender of the child, suspected medicine and type of reported ADR. A total of 429 ADRs were reported for psychotropic medicines and 56% of these were classified as serious. Almost 20% of psychotropic ADRs were reported for children from birth up to 2 years of age and one half of ADRs were reported in adolescents, especially for antidepressants and psychostimulants. Approximately 60% of ADRs were reported for boys. Forty percent of all ADRs were from the category 'nervous and psychiatric disorders'. All but one ADR reported for children below two years were serious and two of these were fatal. A number of serious ADRs reported in children from birth up to 2 years of age were presumably caused by mothers' use of psychotropic medicines during pregnancy.</p> <p>Conclusion</p> <p>The high number of serious ADRs reported for psychotropic medicines in the paediatric population should be a concern for health care professionals and physicians. Considering the higher number of birth defects being reported greater care has to be given while prescribing these drugs for pregnant women.</p

Near-Source Ground Motions from Simulations of Sustained Intersonic and Supersonic Fault Ruptures

We examine the long-period near-source ground motions from simulations of M 7.4 events on a strike-slip fault using kinematic ruptures with rupture speeds that range from subshear speeds through intersonic speeds to supersonic speeds. The strong along-strike shear-wave directivity present in scenarios with subshear rupture speeds disappears in the scenarios with ruptures propagating faster than the shear-wave speed. Furthermore, the maximum horizontal displacements and velocities rotate from generally fault-perpendicular orientations at subshear rupture speeds to generally fault-parallel orientations at supersonic rupture speeds. For rupture speeds just above the shear-wave speed, the orientations are spatially heterogeneous as a result of the random nature of our assumed slip model. At locations within a few kilometers of the rupture, the time histories of the polarization of the horizontal motion provide a better diagnostic with which to gauge the rupture speed than the orientation of the peak motion. Subshear ruptures are associated with significant fault-perpendicular motion before fault-parallel motion close to the fault; supershear ruptures are associated with fault-perpendicular motion after significant fault-parallel motion. Consistent with previous studies, we do not find evidence for prolonged supershear rupture in the long-period (>2 sec) ground motions from the 1979 Imperial Valley earthquake. However, we are unable to resolve the issue of whether a limited portion of the rupture (approximately 10 km in length) propagated faster than the shear-wave speed. Additionally, a recording from the 2002 Denali fault earthquake does appear to be qualitatively consistent with locally supershear rupture. Stronger evidence for supershear rupture in earthquakes may require very dense station coverage in order to capture these potentially distinguishing traits

Constraining fault constitutive behavior with slip and stress heterogeneity

We study how enforcing self-consistency in the statistical properties of the preshear and postshear stress on a fault can be used to constrain fault constitutive behavior beyond that required to produce a desired spatial and temporal evolution of slip in a single event. We explore features of rupture dynamics that (1) lead to slip heterogeneity in earthquake ruptures and (2) maintain these conditions following rupture, so that the stress field is compatible with the generation of aftershocks and facilitates heterogeneous slip in subsequent events. Our three-dimensional finite element simulations of magnitude 7 events on a vertical, planar strike-slip fault show that the conditions that lead to slip heterogeneity remain in place after large events when the dynamic stress drop (initial shear stress) and breakdown work (fracture energy) are spatially heterogeneous. In these models the breakdown work is on the order of MJ/m^2, which is comparable to the radiated energy. These conditions producing slip heterogeneity also tend to produce narrower slip pulses independent of a slip rate dependence in the fault constitutive model. An alternative mechanism for generating these confined slip pulses appears to be fault constitutive models that have a stronger rate dependence, which also makes them difficult to implement in numerical models. We hypothesize that self-consistent ruptures could also be produced by very narrow slip pulses propagating in a self-sustaining heterogeneous stress field with breakdown work comparable to fracture energy estimates of kJ/M^2

Numerical modeling including hysteresis properties for CO2 storage in Tubåen formation, Snøhvit field, Barents Sea

AbstractIn April 2008 the first injection of supercritical CO2 started into the Tubåen Formation from the Snøhvit field, Barents Sea. At full capacity, the plan is to inject approximately 23 Mtons of CO2 via one well during a 30 year period. The aim of this study was to simulation the 30 years of injection of supercritical CO2 and the following long term (5000 years) storage of CO2 in the Tubåen formation. The formation is at approximately 2600 meters depth and is at 98 °C and 265 bars. The simulations suggested that, because of limited lateral permeability, the bottom hole pressure increases rapidly to more than 800 bars if an annual injection rate of 766000 tons is used. This is significantly higher than the fracture pressures for the formation, and it is therefore suggested that the aim to inject 23 Mtons over the planed 30 years may be unrealistic. To prevent fracturing due to increasing pressure, the bottom hole pressure constraint is applied that leads to significant decrease in the amount of CO2 injected. With the hysteresis property applied, reservoir pressure behavior is the same in the base case (no hysteresis); however, the CO2 plume is distributed over a smaller area than in the base case. Similar to the case of hysteresis, the diffusion flow case shows the CO2 plume to be distributed over a smaller area than in the base case, but reservoir pressure decreases more than in the other two cases

Formation and propagation of great salinity anomalies

North Atlantic/Arctic ocean and sea ice variability for the period 1948–2001 is studied using a global Ocean General Circulation Model coupled to a dynamic/thermodynamic sea ice model forced by daily NCEP/NCAR reanalysis data [Kalnay et al., 1996]. Variability of Arctic sea ice properties is analysed, in particular the formation and propagation of sea ice thickness anomalies that are communicated via Fram Strait into the North Atlantic. These export events led to the Great Salinity Anomalies (GSA) of the 1970s, 1980s and 1990s in the Labrador Sea (LS). All GSAs were found to be remotely excited in the Arctic, rather than by local atmospheric forcing over the LS. Sea ice and fresh water exports through the Canadian Archipelago (CAA) are found to be only of minor importance, except for the 1990s GSA. Part of the anomalies are tracked to the Newfoundland Basin, where they enter the North Atlantic Current. The experiments indicate only a minor impact of a single GSA event on the strength of the North Atlantic Thermohaline Circulation (THC)

The formal verification of a pipelined double-precision IEEE floating-point multiplier

Floating-point circuits are notoriously difficult to design and verify. For verification, simulation barely offers adequate coverage, conventional model-checking techniques are infeasible, and theorem-proving based verification is not sufficiently mature. In this paper we present the formal verification of a radix-eight, pipelined, IEEE double-precision floating-point multiplier. The verification was carried out using a mixture of model-checking and theorem-proving techniques in the Voss hardware verification system. By combining model-checking and theorem-proving we were able to build on the strengths of both areas and achieve significant results with a reasonable amount of effort.

Effects of Fault Dip and Slip Rake Angles on Near-Source Ground Motions: Why Rupture Directivity Was Minimal in the 1999 Chi-Chi, Taiwan, Earthquake

We study how the fault dip and slip rake angles affect near-source ground velocities and displacements as faulting transitions from strike-slip motion on a vertical fault to thrust motion on a shallow-dipping fault. Ground motions are computed for five fault geometries with different combinations of fault dip and rake angles and common values for the fault area and the average slip. The nature of the shear-wave directivity is the key factor in determining the size and distribution of the peak velocities and displacements. Strong shear-wave directivity requires that (1) the observer is located in the direction of rupture propagation and (2) the rupture propagates parallel to the direction of the fault slip vector. We show that predominantly along-strike rupture of a thrust fault (geometry similar in the Chi-Chi earthquake) minimizes the area subjected to large-amplitude velocity pulses associated with rupture directivity, because the rupture propagates perpendicular to the slip vector; that is, the rupture propagates in the direction of a node in the shear-wave radiation pattern. In our simulations with a shallow hypocenter, the maximum peak-to-peak horizontal velocities exceed 1.5 m/sec over an area of only 200 km^2 for the 30°-dipping fault (geometry similar to the Chi-Chi earthquake), whereas for the 60°- and 75°-dipping faults this velocity is exceeded over an area of 2700 km^2. These simulations indicate that the area subjected to large-amplitude long-period ground motions would be larger for events of the same size as Chi-Chi that have different styles of faulting or a deeper hypocenter