Randomized Polypill Crossover Trial in People Aged 50 and Over

PMCID: PMC3399742This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

Foreshocks and Aftershocks of the Great 1857 California Earthquake

The San Andreas fault is the longest fault in California and one of the longest strike-slip faults anywhere in the world, yet we know little about many aspects of its behavior before, during, and after large earthquakes. We conducted a study to locate and to estimate magnitudes for the largest foreshocks and aftershocks of the 1857 M 7.9 Fort Tejon earthquake on the central and southern segments of the fault. We began by searching archived first-hand accounts from 1857 through 1862, by grouping felt reports temporally, and by assigning modified Mercalli intensities to each site. We then used a modified form of the grid-search algorithm of Bakun and Wentworth, derived from empirical analysis of modern earthquakes, to find the location and magnitude most consistent with the assigned intensities for each of the largest events. The result confirms a conclusion of Sieh that at least two foreshocks (“dawn” and “sunrise”) located on or near the Parkfield segment of the San Andreas fault preceded the mainshock. We estimate their magnitudes to be M ≈ 6.1 and M ≈ 5.6, respectively. The aftershock rate was below average but within one standard deviation of the number of aftershocks expected based on statistics of modern southern California mainshock-aftershock sequences. The aftershocks included two significant events during the first eight days of the sequence, with magnitudes M ≈ 6.25 and M ≈ 6.7, near the southern half of the rupture; later aftershocks included a M ≈ 6 event near San Bernardino in December 1858 and a M ≈ 6.3 event near the Parkfield segment in April 1860. From earthquake logs at Fort Tejon, we conclude that the aftershock sequence lasted a minimum of 3.75 years

Reconciling the Evidence on Serum Homocysteine and Ischaemic Heart Disease: A Meta-Analysis

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Spatial and temporal distribution of slip for the 1992 Landers, California, earthquake

We have determined a source rupture model for the 1992 Landers earthquake (M_W 7.2) compatible with multiple data sets, spanning a frequency range from zero to 0.5 Hz. Geodetic survey displacements, near-field and regional strong motions, broadband teleseismic waveforms, and surface offset measurements have been used explicitly to constrain both the spatial and temporal slip variations along the model fault surface. Our fault parameterization involves a variable-slip, multiple-segment, finite-fault model which treats the diverse data sets in a self-consistent manner, allowing them to be inverted both independently and in unison. The high-quality data available for the Landers earthquake provide an unprecedented opportunity for direct comparison of rupture models determined from independent data sets that sample both a wide frequency range and a diverse spatial station orientation with respect to the earthquake slip and radiation pattern. In all models, consistent features include the following: (1) similar overall dislocation patterns and amplitudes with seismic moments of 7 to 8 × 10^(26) dyne-cm (seismic potency of 2.3 to 2.7 km^3); (2) very heterogeneous, unilateral strike slip distributed over a fault length of 65 km and over a width of at least 15 km, though slip is limited to shallower regions in some areas; (3) a total rupture duration of 24 sec and an average rupture velocity of 2.7 km/sec; and (4) substantial variations of slip with depth relative to measured surface offsets. The extended rupture length and duration of the Landers earthquake also allowed imaging of the propagating rupture front with better resolution than for those of prior shorter-duration, strike-slip events. Our imaging allows visualization of the rupture evolution, including local differences in slip durations and variations in rupture velocity. Rupture velocity decreases markedly at shallow depths, as well as near regions of slip transfer from one fault segment to the next, as rupture propagates northwestward along the multiply segmented fault length. The rupture front slows as it reaches the northern limit of the Johnson Valley/Landers faults where slip is transferred to the southern Homestead Valley fault; an abrupt acceleration is apparent following the transfer. This process is repeated, and is more pronounced, as slip is again passed from the northern Homestead Valley fault to the Emerson fault. Although the largest surface offsets were observed at the northern end of the rupture, our modeling indicates that substantial rupture was also relatively shallow (less than 10 km) in this region

Slip distribution and tectonic implication of the 1999 Chi‐Chi, Taiwan, Earthquake

We report on the fault complexity of the large (M_w = 7.6) Chi‐Chi earthquake obtained by inverting densely and well‐distributed static measurements consisting of 119 GPS and 23 doubly integrated strong motion records. We show that the slip of the Chi-Chi earthquake was concentrated on the surface of a ”wedge shaped” block. The inferred geometric complexity explains the difference between the strike of the fault plane determined by long period seismic data and surface break observations. When combined with other geophysical and geological observations, the result provides a unique snapshot of tectonic deformation taking place in the form of very large (>10m) displacements of a massive wedge‐shaped crustal block which may relate to the changeover from over‐thrusting to subducting motion between the Philippine Sea and the Eurasian plates

Source Description of the 1999 Hector Mine, California, Earthquake, Part I: Wavelet Domain Inversion Theory and Resolution Analysis

We present a new procedure for the determination of rupture complexity from a joint inversion of static and seismic data. Our fault parameterization involves multiple fault segments, variable local slip, rake angle, rise time, and rupture velocity. To separate the spatial and temporal slip history, we introduce a wavelet transform that proves effective at studying the time and frequency characteristics of the seismic waveforms. Both data and synthetic seismograms are transformed into wavelets, which are then separated into several groups based on their frequency content. For each group, we use error functions to compare the wavelet amplitude variation with time between data and synthetic seismograms. The function can be an L1 + L2 norm or a correlative function based on the amplitude and scale of wavelet functions. The objective function is defined as the weighted sum of these functions. Subsequently, we developed a finite-fault inversion routine in the wavelet domain. A simulated annealing algorithm is used to determine the finite-fault model that minimizes the objective function described in terms of wavelet coefficients. With this approach, we can simultaneously invert for the slip amplitude, slip direction, rise time, and rupture velocity efficiently. Extensive experiments conducted on synthetic data are used to assess the ability to recover rupture slip details. We, also explore slip-model stability for different choices of layered Earth models assuming the geometry encountered in the 1999 Hector Mine, California, earthquake

Source Description of the 1999 Hector Mine, California, Earthquake, Part II: Complexity of Slip History

We present a rupture model of the Hector Mine earthquake (M 7.1), determined from the joint inversion of strong-motion records, P and SH teleseismic body waves, Global Positioning System (GPS) displacement vectors, and measured surface offset. We solve for variable local slip, rake angle, rise time, and rupture velocity of a finite-fault model involving multiple segments. The inversion methodology developed in a companion article (Ji et al., 2002) combines a wavelet transform approach with a nonlinear (simulated annealing) algorithm. The final model is checked by forward simulating the Interferometric Synthetic Aperture Radar (InSar) data. Our estimation to the seismic moment is 6.28 × 10^(19) N m, which is distributed along three segments from north to south, releasing 37%, 41%, and 22% of the total moment, respectively. The average slip is 1.5 m, with peak amplitudes as high as 7 m. The fault rupture has an average rise time of 3.5 sec and a relatively slow average rupture velocity (1.9 km/sec) resulting in a 14-sec rupture propagation history. Our approach permits large variation in rupture velocity and rise time, and indicates that rise time appears to be roughly proportional to slip and shorter rise times are associated with the initiation of asperity rupture. We also find evidence for nearly simultaneous rupture of the two northern branches

Basin Structure Estimation by Waveform Modeling: Forward and Inverse Methods

We introduce a technique for using broadband seismograms recorded from earthquakes at local and regional distances to refine basin structure. For the region outside the basin, we assume a one-dimensional (1D) crustal model and analytical techniques (GRT) to propagate the energy from sources to the basin edge where the motions are then interfaced with a (2D) finite-difference algorithm (Wen and Helmberger, 1996). We parameterize the basin section by isovelocity layers with linear dipping segments between control points. The control point depths are allowed to vary to improve the modeling of waveform data of stations inside the basin. The comparison between data and synthetics is qualified by a fitness function defined by two factors; the timing shift required for best alignment and the correlation coefficient. The procedure was applied to a strong-motion waveform profile across the extended Los Angeles Basin produced by the 1992 Landers, California earthquake to refine the velocity structure using sensitivity testing and forward modeling. Only the correlation coefficient and amplitude were used because absolute timing was unknown. The procedure was extended to a direct waveform inversion by employing a conjugate gradient approach, which uses numerical derivatives. Numerical tests using the new inversion process with synthetic data demonstrate that it is possible to recover a detailed basin structure, if a sufficient amount of high-quality data exists

A simple expression for the ADM mass

We show by an almost elementary calculation that the ADM mass of an asymptotically flat space can be computed as a limit involving a rate of change of area of a closed 2-surface. The result is essentially the same as that given by Brown and York. We will prove this result in two ways, first by direct calculation from the original formula as given by Arnowitt, Deser and Misner and second as a corollary of an earlier result by Brewin for the case of simplicial spaces.Comment: 9 pages, 1 figur

Strong-Motion and Broadband Teleseismic Analysis of the Earthquake for Rupture Process and Hazards Assessment

We have used broadband records from 18 teleseismic stations and three-component records from 16 local strongmotion stations in a formal inversion to determine the temporal and spatial distribution of slip during the earthquake. Separate inversions of the teleseismic (periods, 3-30 s) and strong-motion (periods, 1-5 s) data sets result in similar source models. The data require bilateral rupture, with relatively little slip in the region directly updip from the hypocenter. Slip is concentrated in two patches: one centered 6 km northwest of the hypocenter at 12-km depth with an average slip amplitude of 250 cm, and the other centered about 5 km southeast of the hypocenter at 16-km depth with an average slip amplitude of 180 cm. This bilateral rupture results in large-amplitude ground motions at sites both to the northwest and southeast along the fault strike. The northwestern patch, however, has a larger seismic moment and overall stress drop and thus is the source of the highest ground-motion velocities, a result consistent with observations. The bilateral rupture also results in relatively moderate ground motion directly updip from the hypocenter, in agreement with the ground motions observed at Corralitos, Calif. Furthermore, there is clear evidence of a foreshock (M~4.5-5.0) or slow rupture nucleation about 2 s before the main rupture; the origin time implied by strong-motion trigger times is systematically nearly 2 s later than that predicted from the high-gain regional-network data. The seismic moment obtained from either or both data sets is about 3.0x10^(26) dyne-cm, and the seismic potency is 0.95 km^3. Our analysis indicates that the rupture model determined from the teleseismic data set alone, independent of the strong-motion data set, is adequate to predict many characteristics of the local-strong-motion recordings