Acceleration strategies for elastic full waveform inversion workflows in 2D and 3D

Full waveform inversion (FWI) is one of the most challenging procedures to obtain quantitative information of the subsurface. For elastic inversions, when both compressional and shear velocities have to be inverted, the algorithmic issue becomes also a computational challenge due to the high cost related to modelling elastic rather than acoustic waves. This shortcoming has been moderately mitigated by using high-performance computing to accelerate 3D elastic FWI kernels. Nevertheless, there is room in the FWI workflows for obtaining large speedups at the cost of proper grid pre-processing and data decimation techniques. In the present work, we show how by making full use of frequency-adapted grids, composite shot lists and a novel dynamic offset control strategy, we can reduce by several orders of magnitude the compute time while improving the convergence of the method in the studied cases, regardless of the forward and adjoint compute kernels used.The authors thank REPSOL for the permission to publish the present research and for funding through the AURORA project. J. Kormann also thankfully acknowledges the computer resources, technical expertise and assistance provided by the Barcelona Supercomputing Center - Centro Nacional de Supercomputacti ´on together with the Spanish Supercomputing Network (RES) through grant FI-2014-2-0009. This project has received funding from the European Union’s Horizon 2020, research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 644202. The research leading to these results has received funding from the European Union’s Horizon 2020 Programme (2014–2020) and from the Brazilian Ministry of Science, Technology and Innovation through Rede Nacional de Pesquisa (RNP) under the HPC4E Project (www.hpc4e.eu), grant agreement no. 689772.We further want to thank the Editor Clint N. Dawson for his help, and Andreas Fichtner and an anonymous reviewer for their comments and suggestions to improve the manuscript.Peer ReviewedPostprint (published version

Fast GPU-Based Seismogram Simulation From Microseismic Events in Marine Environments Using Heterogeneous Velocity Models

A novel approach is presented for fast generation of synthetic seismograms due to microseismic events, using heterogeneous marine velocity models. The partial differential equations (PDEs) for the 3D elastic wave equation have been numerically solved using the Fourier domain pseudo-spectral method which is parallelizable on the graphics processing unit (GPU) cards, thus making it faster compared to traditional CPU based computing platforms. Due to computationally expensive forward simulation of large geological models, several combinations of individual synthetic seismic traces are used for specified microseismic event locations, in order to simulate the effect of realistic microseismic activity patterns in the subsurface. We here explore the patterns generated by few hundreds of microseismic events with different source mechanisms using various combinations, both in event amplitudes and origin times, using the simulated pressure and three component particle velocity fields via 1D, 2D and 3D seismic visualizations.Shell Projects and Technolog

Resolving Wave Propagation in Anisotropic Poroelastic Media Using Graphical Processing Units (GPUs)

Biot's equations describe the physics of hydromechanically coupled systems establishing the widely recognized theory of poroelasticity. This theory has a broad range of applications in Earth and biological sciences as well as in engineering. The numerical solution of Biot's equations is challenging because wave propagation and fluid pressure diffusion processes occur simultaneously but feature very different characteristic time scales. Analogous to geophysical data acquisition, high resolution and three dimensional numerical experiments lately redefined state of the art. Tackling high spatial and temporal resolution requires a high-performance computing approach. We developed a multi- graphical processing units (GPU) numerical application to resolve the anisotropic elastodynamic Biot's equations that relies on a conservative numerical scheme to simulate, in a few seconds, wave fields for spatial domains involving more than 1.5 billion grid cells. We present a comprehensive dimensional analysis reducing the number of material parameters needed for the numerical experiments from ten to four. Furthermore, the dimensional analysis emphasizes the key material parameters governing the physics of wave propagation in poroelastic media. We perform a dispersion analysis as function of dimensionless parameters leading to simple and transparent dispersion relations. We then benchmark our numerical solution against an analytical plane wave solution. Finally, we present several numerical modeling experiments, including a three-dimensional simulation of fluid injection into a poroelastic medium. We provide the Matlab, symbolic Maple, and GPU CUDA C routines to reproduce the main presented results. The high efficiency of our numerical implementation makes it readily usable to investigate three-dimensional and high-resolution scenarios of practical applications.ISSN:2169-9313ISSN:0148-0227ISSN:2169-935

Isparta havza yapısının jeofizik yöntemler ile modellenmesi ve senaryo deprem sismik tehlike haritalarının hazırlanması

06.03.2018 tarihli ve 30352 sayılı Resmi Gazetede yayımlanan “Yükseköğretim Kanunu İle Bazı Kanun Ve Kanun Hükmünde Kararnamelerde Değişiklik Yapılması Hakkında Kanun” ile 18.06.2018 tarihli “Lisansüstü Tezlerin Elektronik Ortamda Toplanması, Düzenlenmesi ve Erişime Açılmasına İlişkin Yönerge” gereğince tam metin erişime açılmıştır.Bu tez çalışmasında, Isparta havzasının senaryo deprem simülasyonun bölgede etkili fayları kullanarak elde edilmesi ve deprem tehlike şiddet dağılımının ortaya çıkarılması amaçlanmıştır. Bunun için öncelikle Isparta havzasının zemin özellikleri ve ana kaya derinlik dağılımı ortaya konmuştur. Bu özelliklerin gerçekleştirilmesi için çeşitli jeofizik yöntemler kullanılmıştır. Bunlar; ReMi, sismik yansıma ve gravite yöntemleridir. 152 noktada toplanan Remi verisinden kayma dalgası hızları (Vs) elde edilmiş ve bu hızlar kullanılarak zemin sınıflandırması NEHRP'e (National Earthquake Hazards Reduction Program) göre yapılmıştır. Piroklastik malzeme ve kuvaterner yaşlı alüvyon çökellerden oluşan basen içi ve kenarı D ve C zemin grupları ile tanımlanmıştır. Diğer taraftan çalışma alanında ana kaya derinlik dağılımın ortaya çıkarılmasında sismik yansıma ve gravite yöntemi karşılaştırmalı olarak kullanılmıştır. Havzaya batıdan ve doğudan 2.1 ve 1.1 km'lik iki profil boyunca sismik yansıma verisi toplanmış ve sismik kesitler elde edilmiştir. Sismik yansıma kesitlerinde havzanın batı kenar derinliği 142 m, doğu kenarı derinliği ise 194 m olarak tespit edilmiştir. Havzanın ana kaya derinlik dağılımı için 108 noktada yaklaşık 1.2 km grid aralığı ile gravite verisi toplanmıştır. Bu veri ile yapılan çözümlemelerde Isparta havzasında alüvyal istif kalınlığı maksimum 511 m olarak belirlenmiştir. Simülasyonda kullanılacak sonlu fay kırıklarının ana kaya derinlik dağılımı oluşturabilmek için MTA'ya ait bouguer gravite verileri kullanılmıştır. Jeofizik yöntemlerden elde edilen tüm sonuçlar senaryo deprem simülasyonuna saha parametresi olarak entegre edilmiştir. Senaryo deprem simülasyonu için, 3 boyutlu elastik dalga yayılım kodu E3D (3-D Elastic Seismic Wave Propagation Code) kullanılmıştır. Simülasyonda Isparta havzası üzerinde etkili olan Fetiye-Burdur fay zonu üzerindeki 3 Ekim 1914 Burdur (Ms=7.0) ve 12 Mayıs 1971 Burdur (Ms=6.0), Dinar-Çivril fayı üzerindeki 1 Ekim 1995 Dinar (Ms=6.2) depremleri dikkate alınmıştır. Bu depremleri üreten sonlu fay segmentlerinin farklı kırılma durumları ve nokta kaynak mekanizmalı 24 Ağustos 2014 Ağlasun (Mw=5.0) depreminin ise tekrarı modellenmiştir. Toplamda 10 farklı senaryo ile Isparta havzasının sismik tehlike şiddet dağılımı ortaya konmuştur. Senaryo simülasyonlar neticesinde 1914-Burdur KD yönlü tek taraflı kırılma modelinde, Isparta havzasında meydana gelecek en büyük yer hızının (Peak Ground Velocity, PGV) 36 cm/sn, aletsel şiddetin ise VIII'e yakın olacağı öngörülmektedir.In this study, it is aimed to reveal earthquake hazard intensity distribution of fault segments affecting Isparta basin south of Isparta angle using scenario earthquake simulation. Primarily, for this purpose, ReMi, seismic reflection and gravity method have been used as geophysical methods in order to reveal the soil properties and bedrock depth distribution of Isparta basin. The ground classification was made according to the National Earthquake Hazards Reduction Program (NEHRP) using the slip wave velocities (Vs) obtained from the Remi study at 152 points. The inside and edge of the basin, composed of pyroclastic material and quaternary alluvial deposits, are defined by D and C ground groups. Seismic reflection and gravity method are used comparatively to reveal the depth distribution of the bedrock in the study area. In the seismic reflection method performed at 200 CDP (Common Depth Point) on two profiles with a total length of 3.2 km, the western edge depth of the basin is determined as 142 m and the eastern edge depth is 194 m. The depth distribution of the basin bedrock was determined by gravity method, which is carried out with a grid interval of approximately 1.2 km at 108 points. Within this context, the highest alluvial deposit thickness in the Isparta basin is 511 m. The bouguer gravity data collected by the MTA were used to generate the main rock depth distribution of the simulation area. The results obtained from geophysical methods are entered as field data for scenario earthquake simulations. In the scenario earthquake simulation, 3-D Elastic Seismic Wave Propagation Code (E3D) was used. In the simulation, 3 October 1914 Burdur (Ms = 7.0) earthquake, 12 May 1971 Burdur (Ms = 6.0) earthquake on the Fethiye-Burdur fault zone and 1 October 1995 Dinar (Ms = 6.2) earthquake on the Dinar-Çivril fault, which are effective on the Isparta basin, were considered. Different rupture states of finite fault segments which are forming these earthquakes are modeled. In addition, 24 August 2014 Ağlasun (Mw = 5.0) point-source mechanism earthquake was modeled. Seismic hazard intensity distribution of Isparta basin is investigated with 10 different scenarios in total. As a result of scenario simulation of the 1914-Burdur NE directional single-sided fracture model, it is predicted that the highest ground speed (Peak Ground Velocity, PGV) will be 36 cm / sec and the instrumental intensity will be close to VIII