An efficient method of 3-D elastic full waveform inversion using a finite-difference injection method for time-lapse imaging

International audienceSeismic full waveform inversion is an objective method to estimate elastic properties of the subsurface and is an important area of research, particularly in seismic exploration community. It is a data-fitting approach, where the difference between observed and synthetic data is minimized iteratively. Due to a very high computational cost, the practical implementation of waveform inversion has so far been restricted to a 2-D geometry with different levels of physics incorporated in it (e.g. elasticity/viscoelasticity) or to a 3-D geometry but using an acoustic approximation. However, the earth is three-dimensional, elastic and heterogeneous and therefore a full 3-D elastic inversion is required in order to obtain more accurate and valuable models of the subsurface. Despite the recent increase in computing power, the application of 3-D elastic full waveform inversion to real-scale problems remains quite challenging on the current computer architecture. Here, we present an efficient method to perform 3-D elastic full waveform inversion for time-lapse seismic data using a finite-difference injection method. In this method, the wavefield is computed in the whole model and is stored on a surface above a finite volume where the model is perturbed and localized inversion is performed. Comparison of the final results using the 3-D finite-difference injection method and conventional 3-D inversion performed within the whole volume shows that our new method provides significant reductions in computational time and memory requirements without any notable loss in accuracy. Our approach shows a big potential for efficient reservoir monitoring in real time-lapse experiments

Hemorrhage from varices in hepaticojejunostomy in the fifth and tenth year after surgery for hepatic hilar bile duct cancer: a case report

We report a case of a 64-year-old female patient who underwent a right lobectomy of the liver (including total resection of the caudate lobe), dissection of the group 2 lymph nodes, left hepaticojejunostomy (Roux-en-Y fashion), and reconstruction of the portal vein (end-to-end anastomosis between the main portal vein and the left portal branch) for treatment of hepatic hilar bile duct cancer in 1996. In 2001, the anastomotic site of the hepaticojejunostomy was dissected and re-anastomosed due to gastrointestinal bleeding caused by variceal rupture in the jejunal loop. In 2006, splenectomy was performed for recurrence of gastrointestinal bleeding due to another variceal rupture in the jejunal loop. Portal venography performed perioperatively showed a decrease in portal blood flow into the liver via the jejunal varices and an increase in portal blood flow into the liver via the left gastric vein. She had two jejunal variceal ruptures at five-year intervals after extrahepatic portal obstruction and underwent successful treatments

Port site herniation of the small bowel following laparoscopy-assisted distal gastrectomy: a case report

<p>Abstract</p> <p>Introduction</p> <p>Port-site herniation is a rare but potentially dangerous complication after laparoscopic surgery. Closure of port sites, especially those measuring 10 mm or more, has been recommended to avoid such an event.</p> <p>Case presentation</p> <p>We herein report the only case of a port site hernia among a series 52 consecutive cases of laparoscopy-assisted distal gastrectomy (LADG) carried out by our unit between July 2002 and March 2007. In this case the small bowel herniated and incarcerated through the port site on day 4 after LADG despite closure of the fascia. Initial manifestations experienced by the patient, possibly due to obstruction, and including mild abdominal pain and nausea, occurred on the third day postoperatively. The definitive diagnosis was made on day 4 based on symptoms related to leakage from the duodenal stump, which was considered to have developed after severe obstruction of the bowel. Re-operation for reduction of the incarcerated bowel and tube duodenostomy with peritoneal drainage were required to manage this complication.</p> <p>Conclusion</p> <p>We present this case report and review of literature to discuss further regarding methods of fascial closure after laparoscopic surgery.</p

First Focal Mechanisms of Marsquakes

Since February 2019, NASA's InSight lander is recording seismic signals on the planet Mars, which, for the first time, allows to observe ongoing tectonic processes with geophysical methods. A number of Marsquakes have been located in the Cerberus Fossae graben system in Elysium Planitia and further west, in the Orcus Patera depression. We present a first study of the focal mechanisms of three well-recorded events (S0173a, S0183a, S0235b) to determine the processes dominating in the source region. We infer for all three events a predominantly extensional setting. Our method is adapted to the case of a single, multicomponent receiver and based on fitting waveforms of P and S waves against synthetic seismograms computed for the initial crustal velocity model derived by the InSight team. We explore the uncertainty due to the single-station limitation and find that even data recorded by one station constrains the mechanisms (reasonably) well. For the events in the Cerberus Fossae region (S0173a, S0235b) normal faulting with a relatively steep dipping fault plane is inferred, suggesting an extensional regime mainly oriented E-W to NE-SW. The fault regime in the Orcus Patera region is not determined uniquely because only the P wave can be used for the source inversion. However, we find that the P and weak S waves of the S0183a event show similar polarities to the event S0173, which indicates similar fault regimes

Pre-mission InSights on the Interior of Mars

Abstract The Interior exploration using Seismic Investigations, Geodesy, and Heat Trans- port (InSight) Mission will focus on Mars’ interior structure and evolution. The basic structure of crust, mantle, and core form soon after accretion. Understanding the early differentiation process on Mars and how it relates to bulk composition is key to improving our understanding of this process on rocky bodies in our solar system, as well as in other solar systems. Current knowledge of differentiation derives largely from the layers observed via seismology on the Moon. However, the Moon’s much smaller diameter make it a poor analog with respect to interior pressure and phase changes. In this paper we review the current knowledge of the thickness of the crust, the diameter and state of the core, seismic attenuation, heat flow, and interior composition. InSight will conduct the first seismic and heat flow measurements of Mars, as well as more precise geodesy. These data reduce uncertainty in crustal thickness, core size and state, heat flow, seismic activity and meteorite impact rates by a factor of 3–10× relative to previous estimates. Based on modeling of seismic wave propagation, we can further constrain interior temperature, composition, and the location of phase changes. By combining heat flow and a well constrained value of crustal thickness, we can estimate the distribution of heat producing elements between the crust and mantle. All of these quantities are key inputs to models of interior convection and thermal evolution that predict the processes that control subsurface temperature, rates of volcanism, plume distribution and stability, and convective state. Collectively these factors offer strong controls on the overall evolution of the geology and habitability of Mars

Educational Effect of School Size and Class Size on Students School Life

Many aspects of school life in public elementary and junior high school was assessed by teachers. The smaller the class size is, the better quality of students' school life, and teachers' guidance. School size is also important for them, especially at junior high school. Class size and school size have more effect on teacher's life guidance than student's discipline

DSM Kernel Suite

This suite of programmes is to calculate 3D finite frequency Fréchet sensitivity kernels (or 3D waveform partial derivatives) for 1D reference Earth models using Direct Solution Method. It consists of forward and back propagated strain Green's function calculation in a 2D plane, cross correlations of forward and back propagated wavefields to obtain sensitivity kernels. We developed also visualisation facilities of kernels. Those who would like to get kernels by comparing observed and synthetic waveforms, we developed python interface for that purpose as well. All the main motors are parallelised and you just have to submit prepared scripts. For more information, please refer to README.m

Three‐dimensional Elastic and Anelastic Structure of the Lowermost Mantle Beneath the Western Pacific From Finite‐Frequency Tomography

International audienceWe build a finite‐frequency tomography method that uses traveltime and amplitude data for obtaining 3‐D maps of shear velocity ( urn:x-wiley:jgrb:media:jgrb54035:jgrb54035-math-0001) and seismic attenuation (measured with the quality factor urn:x-wiley:jgrb:media:jgrb54035:jgrb54035-math-0002). We then apply this method to recover the 3‐D urn:x-wiley:jgrb:media:jgrb54035:jgrb54035-math-0003 and urn:x-wiley:jgrb:media:jgrb54035:jgrb54035-math-0004 structures in the lowermost mantle beneath the western edge of the Pacific large low shear velocity province, using the urn:x-wiley:jgrb:media:jgrb54035:jgrb54035-math-0005 and urn:x-wiley:jgrb:media:jgrb54035:jgrb54035-math-0006 phases for 31 earthquakes that occurred underneath the vicinity of Tonga and Fiji regions. Our data set consists of the transverse components of 1,341 traces from the Japanese F‐net seismic station network. The waveform data are applied with a band‐pass filter in the period range of 12.5–200 s, corresponding to the frequency range of 0.005–0.08 Hz. Both urn:x-wiley:jgrb:media:jgrb54035:jgrb54035-math-0007 and urn:x-wiley:jgrb:media:jgrb54035:jgrb54035-math-0008 are lower than those in the Preliminary reference Earth model (PREM) in the bottom depth range, with the lowest part being situated at the center of the region we sample. This feature is robust across a variety of inversion configurations. We then estimate possible temperature anomalies in this region from the obtained urn:x-wiley:jgrb:media:jgrb54035:jgrb54035-math-0009 and urn:x-wiley:jgrb:media:jgrb54035:jgrb54035-math-0010 structures. Discrepancy between the temperature anomalies predicted by these two quantities suggests that explaining simultaneously urn:x-wiley:jgrb:media:jgrb54035:jgrb54035-math-0011 and urn:x-wiley:jgrb:media:jgrb54035:jgrb54035-math-0012 anomalies in this region requires both temperature and chemical anomalies. Assuming that urn:x-wiley:jgrb:media:jgrb54035:jgrb54035-math-0013 anomalies are a reliable proxy for temperature and that compositional anomalies primarily consist of an excess in iron oxide, we propose a possible thermal and compositional structure for this region