Low-velocity zone atop the 410-km seismic discontinuity in the northwestern United States

The seismic discontinuity at 410 km depth in the Earth's mantle is generally attributed to the phase transition of (Mg,Fe)_2SiO_4 from the olivine to wadsleyite structure. Variation in the depth of this discontinuity is often taken as a proxy for mantle temperature owing to its response to thermal perturbations. For example, a cold anomaly would elevate the 410-km discontinuity, because of its positive Clapeyron slope, whereas a warm anomaly would depress the discontinuity. But trade-offs between seismic wave-speed heterogeneity and discontinuity topography often inhibit detailed analysis of these discontinuities, and structure often appears very complicated. Here we simultaneously model seismic refracted waves and scattered waves from the 410-km discontinuity in the western United States to constrain structure in the region. We find a low-velocity zone, with a shear-wave velocity drop of 5%, on top of the 410-km discontinuity beneath the northwestern United States, extending from southwestern Oregon to the northern Basin and Range province. This low-velocity zone has a thickness that varies from 20 to 90 km with rapid lateral variations. Its spatial extent coincides with both an anomalous composition of overlying volcanism and seismic 'receiver-function' observations observed above the region. We interpret the low-velocity zone as a compositional anomaly, possibly due to a dense partial-melt layer, which may be linked to prior subduction of the Farallon plate and back-arc extension. The existence of such a layer could be indicative of high water content in the Earth's transition zone

The 25 November 1988 Saguenay, Quebec, Earthquake: Source Parameters and the Attenuation of Strong Ground Motion

The Saguenay earthquake of 25 November 1988 occurred close to the southern margin of the Saguenay Graben in southern Quebec. It was caused by almost purely dip-slip faulting centered at a depth of 26 km with a P axis oriented northeast-southwest. This faulting mechanism is similar to those of the larger historical earthquakes in eastern North America, but the focal depth is substantially greater than all but one of these events. The seismic moment estimated from regional PnI waves and teleseismic long-period body waves is 5 × 10^(24) dyne-cm., corresponding to a moment magnitude of 5.8. The source duration of the earthquake is estimated to be 1.8 sec, corresponding to a stress drop of 160 bars, which is not significantly higher than the average stress drop of 120 bars estimated from previous large earthquakes in eastern North America. In order to simultaneously match the recorded ground motion amplitudes of strong-motion acceleration, strong-motion velocity, and teleseismic short-period and long-period body waves, it is necessary to use a source function having a complex shape that implies the presence of asperities and larger local stress drops. The large set of strong-motion recordings of the Saguenay earthquake has been used to validate a procedure for estimating strong ground motion attenuation based on a simple wave propagation model. The most important feature of the recorded strong motions is that their peak amplitudes do not decay significantly with distance inside 120 km, but then decay abruptly beyond 120 km. Profiles of recorded accelerograms with absolute times indicate that at distances beyond 64 km the peak ground motions are due to strong postcritical reflections from velocity gradients in the lower crust. The principal shear-wave arrivals and the variation of their peak amplitudes with distance were reproduced in synthetic seismograms generated using a regional crustal structure model. The critical distances for the postcritical reflections were short because of the deep focal depth of the event, causing the elevation of ground motion amplitudes out to 120 km. Similar studies of earthquakes in other regions of eastern North America indicate that the strength of the postcritical reflections, and the distance ranges over which they are dominant, are controlled by the focal depth and crustal structure. Regional variations in crustal structure thus give rise to predictable regional variations in strong ground motion attenuation

Are serial CA 19-9 kinetics helpful in predicting survival in patients with advanced or metastatic pancreatic cancer treated with gemcitabine and cisplatin?

Background: Serial kinetics of serum CA 19-9 levels have been reported to reflect response and survival in patients with pancreatic cancer undergoing surgery, radiotherapy, and chemotherapy. We prospectively studied serial kinetics of serum CA 19-9 levels of patients with locally advanced or metastatic disease treated with gemcitabine and cisplatin. Patients and Methods: Enrolled in the study were 87 patients (female/male = 26/61; stage III/IV disease = 24/63). Patients received gemcitabine 1,000 mg/m(2) on days 1, 8, and 15 plus cisplatin 50 mg/m(2) on days 1 and 15, every 4 weeks. Serum samples were collected at the onset of chemotherapy and before the start of a new treatment cycle (day 28). Results: 77 of 87 patients (88.5%) with initially elevated CA 19-9 levels were included for evaluation. According to imaging criteria, 4 (5.2%) achieved a complete remission and 11 (14.3%) achieved partial remission, yielding an overall response rate of 19.5%. 43 (55.8%) patients were CA 19-9 responders, defined by greater than or equal to50% decrease in CA 19-9 serum levels within 2 months after treatment initiation. Except for one, all patients who had responded by imaging criteria (n = 14) fulfilled the criterion of a CA 19-9 responder. Despite being characterized as non-responders by CT-imaging criteria (stable/progressive disease), 29 patients were classified as CA 19-9 responders (positive predictive value 32.5%). Independent of the response evaluation by CT, CA 19-9 responders survived significantly longer than CA 19-9 non-responders (295 d; 95% CI: 285-445 vs. 174 d; 95% CI: 134-198; p = 0.022). Conclusion: CA 19-9 kinetics in serum serve as an early and reliable indicator of response and help to predict survival in patients with advanced pancreatic cancer receiving effective treatment with gemcitabine and cisplatin

The effect of crustal structure on strong ground motion attenuation relations in eastern North America

Strong ground motion attenuation relations are usually described by smoothly decreasing functions of distance. However, consideration of wave propagation in the crust suggests that attenuation relations should be more complex. Such complexity may be present in strong ground motion data for eastern North American earthquakes, which show amplitudes in the distance range of 60 to 150 km that lie above the trends at smaller and greater distances. Using a wavenumber integration method to compute Green's functions and close-in recordings of several earthquakes as empirical source functions, we have generated synthetic seismograms that are in good agreement with regional and strong-motion recordings of eastern North American earthquakes. From these synthetic seismograms, we have shown that the observed interval of relatively high amplitudes may be attributable to postcritically reflected S waves from the Moho. The presence and location of the interval of relatively high amplitudes is highly dependent on the crustal velocity structure and may therefore be expected to show regional variation. However, for any realistic structure model, there will be a transition in the attenuation relation from an interval at shorter distances (less than about 100 km) that is dominated by direct waves to an interval at greater distances that is dominated by postcritically reflected waves. The synthetic seismograms have response spectral velocities that match those of the recorded data, and their m_(bLg) values are in good agreement with observed values

The Location and Source Parameters of the Lompoc, California, Earthquake of 4 November 1927

In this paper, we address the relocation, magnitudes, and the style of faulting of the Lompoc earthquake from a sparse assortment of teleseismic and regional seismograms. The highest quality teleseismic waveform data come from a station at De Bilt (Netherlands) that remains in operation. Thus, recordings of numerous modern events in central coastal California (i.e., the 1969 Santa Lucia Banks, 1983 Coalinga, 1978 Santa Barbara, and 1989 Loma Prieta earthquakes) have been used for comparison with the 1927 records. Location constraints for the Lompoc event were established from the De Bilt recording by comparing S-P and SSS-S waveform matches against the above master events to avoid the effect of unknown clock errors on locations that use absolute times. These same seismograms were modeled to estimate the depth, faulting parameters, and source strength. A similar approach using observational comparisons and numerical modeling was applied to the regional waveform data obtained from the stations at Berkeley, Tucson, and Pasadena. Our results indicate a north-northwesterly striking reverse event located about 40 km west of Point Conception, which is in excellent agreement with the recent tsunami modeling results by Satake and Somerville (1992). This location is 25 km south of that proposed by Hanks (1979) and well within his error bars. We obtain a body-wave moment of 1 × 10^(26) dyne-cm, a trapezoidal time history of (2, 2, 2) sec. and a source depth of 10 km. The weak beginning of the Pnl wavetrain at Berkeley indicates some source complexity, which is characteristic of many large events. The fault parameters are strike = N20°W, dip = 66°NE, and rake = 95°. Most seismicity catalogs report a M_s = 7.3 for this event, after Gutenberg and Richter (1956), but this was a long-period body-wave magnitude and not a surface-wave result. Their original worksheets indicate a smaller Ms = 7.0. The body waves of the Loma Prieta event (M_s = 7.1) appear distinctly larger than those of the Lompoc event at De Bilt, in agreement with our lower estimate of source strength

The comparison of grey-scale ultrasonic and clinical features of hepatoblastoma and hepatocellular carcinoma in children: a retrospective study for ten years

<p>Abstract</p> <p>Background</p> <p>Hepatoblastoma (HBL) and hepatocellular carcinoma (HCC) are respectively the first and the second most common pediatric malignant liver tumors. The purpose of this study was to evaluate the combined use of the ultrasound examination and the assessment of the patients' clinical features for differentiating HBL from HCC in children.</p> <p>Methods</p> <p>Thirty cases of the confirmed HBL and 12 cases of the confirmed HCC in children under the age of 15 years were enrolled into our study. They were divided into the HBL group and the HCC group according to the histological types of the tumors. The ultrasonic features and the clinical manifestations of the two groups were retrospectively analyzed, with an emphasis on the following parameters: onset age, gender (male/female) ratio, positive epatitis-B-surface-antigen (HBV), alpha-fetoprotein increase, and echo features including septa, calcification and liquefaction within the tumors.</p> <p>Results</p> <p>Compared with the children with HCC, the children with HBL had a significantly younger onset age (8.2 years vs. 3.9 years, P < 0.001) and a significantly smaller frequency of positive HBV (66.7% vs. 13.3%, P < 0.001). The septa and liquefaction were more frequently found in HBL than in HCC (25/30, 83.3% vs. 2/12, 16.7%, P < 0.001; 17/30, 56.7% vs. 3/12, 25%, P = 0.02). When a combination of the liquefaction, septa, negative HBV and onset age smaller than 5 years was used in the evaluation, the sensitivity was raised to 90%, the accuracy was raised to 88%, and the negative predictive value was raised to 73%.</p> <p>Conclusion</p> <p>Ultrasonic features combined with clinical manifestations are valuable for differentiating HBL from HCC in children.</p