Deep mantle structure and the postperovskite phase transition

Seismologists have known for many years that the lowermost mantle of the Earth is complex. Models based on observed seismic phases sampling this region include relatively sharp horizontal discontinuities with strong zones of anisotropy, nearly vertical contrasts in structure, and small pockets of ultralow velocity zones (ULVZs). This diversity of structures is beginning to be understood in terms of geodynamics and mineral physics, with dense partial melts causing the ULVZs and a postperovskite solid–solid phase transition producing regional layering, with the possibility of large-scale variations in chemistry. This strong heterogeneity has significant implications on heat transport out of core, the evolution of the magnetic field, and magnetic field polarity reversals

Seismological support for the metastable superplume model, sharp features, and phase changes within the lower mantle

Recently, a metastable thermal-chemical convection model was proposed to explain the African Superplume. Its bulk tabular shape remains relatively stable while its interior undergoes significant stirring with low-velocity conduits along its edges and down-welling near the middle. Here, we perform a mapping of chemistry and temperature into P and S velocity variations and replace a seismically derived structure with this hybrid model. Synthetic seismogram sections generated for this 2D model are then compared directly with corresponding seismic observations of P (P, PCP, and PKP) and S (S, SCS, and SKS) phases. These results explain the anticorrelation between the bulk velocity and shear velocity and the sharpness and level of SKS travel time delays. In addition, we present evidence for the existence of a D" triplication (a putative phase change) beneath the down-welling structure

Simulation of strong ground motions

The estimation of potential strong ground motions at short epicentral distances (Δ = 10 to 25 km) resulting from large earthquakes, M ≧ 6.5, generally requires extrapolation of a limited data set. The goal of this project has been to quantify the extrapolation through a simulation technique that relies heavily upon the more extensive data set from smaller magnitude earthquakes. The simulation utilizes the smaller events as Green's functions for the elements of a larger fault. Comparison of the simulated peak acceleration and duration with the data from the Parkfield earthquake is very good. Simulation of three earthquakes, M = 5.5, 6.5, and 7.0 indicate that the slope of the peak acceleration versus distance curve (Δ = 5 to 25 km) flattens, for strike-slip earthquakes, as the magnitude increases

Seismic source functions and attenuation from local and teleseismic observations of the NTS events Jorum and Handley

Several strong-motion seismograms recorded at 8 km from a large nuclear test at Pahute Mesa, Nevada Test Site, are modeled using the Cagniard-de Hoop technique. The ratio of vertical to radial motions suggest that the peak values are produced by ray paths that penetrated to a depth several kilometers below the source. A homogeneous layered Earth model with velocity increasing with depth was used in the modeling of the velocity time histories. The upper portion of the velocity model was determined by averaging bore-hole data and the lower portion was obtained from regional refraction measurements. Assuming a modified Haskell (1967) source representation, ψ(t) = ψ_o[1 - e^(-Kt)(1 + Kt (Kt)^2/2 - B(Kt)^3)] we obtain a range of source descriptions with ψ_o varying with K and B, ψ_o (K,B). The range of source models for Jorum are ψ_o (5, 1) = 3.1, ψ_o (5, 2) = 1.7, and ψ_o (5, 3) = 1.2 times 10^(11) cm^3, respectively. Given an explosion source description, it is a straightforward task to determine the teleseismic attenuation from WWSSN observations. From both the short- and long-period observations from these events, an average t^* of 1.3 is obtained for compressional waves of a dominant 1-sec period. This estimate is insensitive to the range of K and B obtained from the near-field modeling

Peak acceleration scaling studies

An acceleration time history can be decomposed into a series of operations that transfers energy from each point on the fault to the recording station ACC(t) = S * R * E * Q where S is the source time function, R represents rupture over a finite fault, E is the elastic propagation through the earth, and Q is the path attenuation, assumed to be linear. If these operators were exactly known, a deterministic approach to predicting strong ground motions would be straightforward. For the current study, E was computed from a velocity model that incorporates a stiff sedimentary layer over a southern California crust. A range of realistic rupture velocities have been obtained by other investigators and is incorporated into the simulation. Assumptions of the path averaged attenuation, Q, can be tested by comparing with observational data, as a function of distance, the parameters peak acceleration, and computed M_L. This provides a check on both the high frequency (∼ 5 Hz) and long-period (∼ 1 sec) behavior of E^* Q. An average curstal shear wave Q_β of 300 is found to be compatible with observational data (M_L = 4.5 to 5.0). Assumptions of S can be avoided by using real sources derived from accelerograms recorded at small epicentral distances (epicentral distance/source depth < 1). Using these operators, accelerograms have been simulated for strike-slip faulting for four magnitudes: 4.5; 5.5; 6.5; and 7.0. The shapes of the derived average peak ground acceleration (PGA) versus distance curves are well described by the simple equation PGA α [R + C(M)]^(−1.75), where R is the closest distance to the fault surface and C(4.5) = 6, C(5.5) = 12, C(6.5) = 22, and C(7.0) = 36 km

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

Pulmonary Vascular Tree Segmentation from Contrast-Enhanced CT Images

We present a pulmonary vessel segmentation algorithm, which is fast, fully automatic and robust. It uses a coarse segmentation of the airway tree and a left and right lung labeled volume to restrict a vessel enhancement filter, based on an offset medialness function, to the lungs. We show the application of our algorithm on contrast-enhanced CT images, where we derive a clinical parameter to detect pulmonary hypertension (PH) in patients. Results on a dataset of 24 patients show that quantitative indices derived from the segmentation are applicable to distinguish patients with and without PH. Further work-in-progress results are shown on the VESSEL12 challenge dataset, which is composed of non-contrast-enhanced scans, where we range in the midfield of participating contestants.Comment: Part of the OAGM/AAPR 2013 proceedings (1304.1876

Major disruption of D″ beneath Alaska

D″ represents one of the most dramatic thermal and compositional layers within our planet. In particular, global tomographic models display relatively fast patches at the base of the mantle along the circum-Pacific which are generally attributed to slab debris. Such distinct patches interact with the bridgmanite (Br) to post-bridgmanite (PBr) phase boundary to generate particularly strong heterogeneity at their edges. Most seismic observations for the D″ come from the lower mantle S wave triplication (Scd). Here we exploit the USArray waveform data to examine one of these sharp transitions in structure beneath Alaska. From west to east beneath Alaska, we observed three different characteristics in D″: (1) the western region with a strong Scd, requiring a sharp δVs = 2.5% increase; (2) the middle region with no clear Scd phases, indicating a lack of D″ (or thin Br-PBr layer); and (3) the eastern region with strong Scd phase, requiring a gradient increase in δVs. To explain such strong lateral variation in the velocity structure, chemical variations must be involved. We suggest that the western region represents relatively normal mantle. In contrast, the eastern region is influenced by a relic slab that has subducted down to the lowermost mantle. In the middle region, we infer an upwelling structure that disrupts the Br-PBr phase boundary. Such an interpretation is based upon a distinct pattern of travel time delays, waveform distortions, and amplitude patterns that reveal a circular-shaped anomaly about 5° across which can be modeled synthetically as a plume-like structure rising about 400 km high with a shear velocity reduction of ~5%, similar to geodynamic modeling predictions of upwellings

Slab Control on the Northeastern Edge of the Mid-Pacific LLSVP near Hawaii

At the core‐mantle boundary, most observed ultralow velocity zones (ULVZs) cluster along the edges of the large low shear velocity provinces (LLSVPs) and provide key information on the composition, dynamics, and evolution of the lower mantle. However, their detailed structure near slab‐like structures beneath the mid‐Pacific remains particularly challenging because of the lack of station coverage. While most studies of ULVZs concentrate on SKS‐complexity, here we report on the multipathing of ScS, which expands the sampling for ULVZs. We find the strongest multipathing along a ULVZ patch located just south of Hawaii and the far northeastern edge of the LLSVP, in a zone ~200 km in width and extending 600 km southward. The anomalous ScS travel times and distorted S_(diff) waveforms further reveal patches interrupted by observed enhanced D″ indicative of slab‐debris influence on the complexity of the northeastern boundary of the mid‐Pacific LLSVP