bluuebunny/crossref_metadata_2025_split huggingface dataset:
Seismogram synthesis for multi-layered media with irregular interfaces by global generalized reflection/transmission matrices method. I. Theory of two-dimensionalSHcase
Authors: Chen Xiao-fei 
Published: September 2021

AbstractIn this paper, we present a new method of seismogram synthesis for multi-layered media with irregular interfaces due to an arbitrary source. This method can be viewed as either an extension of the T matrix method for an inclusion to multi-layered media by introducing the global generalized R/T matrices, or an extension of the generalized R/T coefficients method for horizontally layered media to irregular layered ones by incorporating the T matrix method. The formulation obtained in this paper is expressed in terms of the global generalized R/T matrices. These global generalized R/T matrices can be determined from integrals along each interface and integral over source area via a recursive relation. This formulation provides an efficient scheme of computation, especially when the number of layers increases. Also, this formulation can be applied to any finite frequency, although for higher frequency it needs more computation time than for lower frequency. As examples, we give solutions of three specific problems, namely, horizontally layered media, irregular topography, and an irregular layer over a half-space.
Correlation of waveforms from closely spaced regional events
Authors: Israelsson Hans 
Published: September 2021

Abstract
We studied the similarity of waveforms recorded at the high frequency element of the NORESS array from 137 events (ML = 0.8 to 2.1) in or near the mining districts of Central Sweden. Waveform correlations based on the covariance matrices of three component recordings and on maximum amplitudes were calculated from traces filtered between 2.5 and 4.0 Hz, in which band the signal-to-noise ratio consistently peaked for the waveforms. A cutoff value for the correlations to separate waveforms with poor and good correlation values could be defined from the statistical uncertainty in back azimuth estimates of NORESS. More than 80 per cent of the events could be grouped with hierarchical clustering into one large group of 98 events and five smaller groups. The NORESS epicenters of the events in the large group were scattered over an area of 20 × 75 km. An exponential decay of the waveform correlation with event separation (d in km) could be fitted to the data of this group (exp(−d/8), taking NORESS epicenter uncertainties into account. A procedure for location of close events based on correlation values is defined. When applied to the large event group it limits the event epicenters to be within an area of about 4 km. For one small event group, high correlation values were obtained above 15 Hz. These frequencies are significantly higher than those reported in other studies, and the so called quarter wavelength argument constrains the event epicenters to within 0.1 km.
Geometrical spreading and Q of Pn waves: An investigative study in eastern Canada
Authors: Zhu Tianfei , Chun Kin-Yip , West Gordon F. 
Published: September 2021

Abstract
Station site effects, uncertainties in seismic source spectrum, and instrument response errors are among the well-known frequency-dependent contaminating factors that limit the reliability of short-period Q measurements of regional phases. For the Pn wave, a regional phase of importance for both magnitude determination and nuclear test ban verification, the problem is made worse by the added uncertainty of its geometric spreading function. For realistic earth models, the Pn geometric spreading function is likely to depart drastically from that expected of canonical head waves. The extent of this departure is sensitively dependent upon the regional crust/mantle structure, making geometric spreading assumption a conspicuous source of disagreement among the published Pn attenuation (QPn) estimates.
We describe a technique, referred to here as the extended reversed two-station method (RTSM), for simultaneous determination of QPn and geometrical spreading function. The formulation, being designed to bring about direct cancellation of the contaminating source, station and instrument effects, is a reliable tool for mapping the Pn propagation characteristics over continental paths, long and short.
The extended RTSM has been tested using Pn spectral amplitude data derived from seismic records of the Eastern Canada Telemetered Network (ECTN). We find the spreading rate coefficient n in the power-law representation of the geometric spreading (d−n, d being epicentral distance) to be frequency dependent, increasing from 1.11 at 1 Hz to 1.77 at 20 Hz. Our QPn model in eastern Canada takes the form of QPn = 189f0.87. The results from eastern Canada suggest that: (a) there exists a significant positive velocity gradient in the uppermost mantle (≧ 0.0037 sec−1); (b) the regionally recorded Pn waves are dominated by the superposition of a series of interfering diving waves bent by the velocity gradient and internally reflected at the underside of the Moho discontinuity; and (c) the very strong frequency-dependence of QPn we found in this study region may not be unique among low-attenuating shield and platform regions.
Spectral yield estimation of NTS explosions
Authors: Taylor Steven R. , Dowla Farid U. 
Published: September 2021

AbstractThe yields of 299 NTS explosions have been estimated from Pn, Pg and Lg spectra (between 0.1 and 10 Hz) at four regional seismic stations. A spectral template matching technique is used where the spectra from an explosion of unknown yield are compared with the spectra of explosions of known yield. A matching function is defined that is a scaled inverse of the difference between the spectra from the known and unknown explosions. The yields from the seven closest matching explosions are then averaged to estimate the yield of the unknown event. The spectral matching technique appears to perform as well as standard regression techniques utilizing mb(Pn) and mb(Lg) measurements except that no geologic information (such as gas-filled porosity) is required. However, the spectral matching technique is only applicable to very well-calibrated test sites. The key to spectral matching is that the spectral shape is sensitive to the near-source geology. In addition to affecting the absolute spectral levels (i.e., coupling), the dynamic response of the near source material to the radiated shock wave is a major factor controlling the shape of the radiated spectra. The spectral shape can therefore be used as an indicator for predicting the coupling of an explosion, which can be subsequently used to predict its yield.
On the accuracy of some approximate antiplane half-space stiffnesses
Authors: Maeda Toshiro , Kausel Eduardo 
Published: September 2021

Abstract
The modeling with discrete methods of elastic media of infinite extent that are subjected to dynamic loads normally calls for the use of special transmitting (or nonreflecting) boundaries. One such discrete method is the thin layer method, which allows efficient computation of the Green's functions for layered soils of finite depth; its application to elastic half-spaces, however, requires that the infinite medium be represented by means of approximations that are analogous to transmitting boundaries. In this article, we explore the accuracy of two of these approximations in the context of the Green's functions for antiplane (or SH) line loads. We find that the paraxial approximation of Engquist - Majda gives good results, provided that a “buffer layer” with the same material properties as the half-space separates the computational domain from the transmitting boundary. While these results were studied from the point of view of the thin layer method, they apply equally well to models with finite elements or finite differences.
The G-calibration: A new method for an absolute in situ calibration of long-period accelerometers, tested on the Streckeisen instruments of the GEOSCOPE network
Authors: Bernard P. , Karczewski J.-F. , Morand M. , Dole B. , Romanowicz B. 
Published: September 2021

Abstract
The sensitivity of the Streckeisen's very broadband (VBB) accelerometers is routinely measured on tilt tables by the manufacturer, with an announced accuracy of about 1 per cent. Nevertheless, the transportation of the station or different in situ environmental conditions may modify the sensitivity. As one may expect that a high accuracy in the wave amplitude will be required in the future by seismologists, we developed and tested an in situ absolute calibration method, which does not require the seismometers to be moved. Its principle is simple: A mass is moving in the vicinity of the force-balance accelerometer, and the perturbation of the gravitational field is measured. This calibration method, because it requires the use of G, the gravitational constant, is termed the G-calibration. At a distance of 0.5 m, the gravitational field of a 30 kg mass is 8 × 10−9 m.sec−2, which is 2 order of magnitude greater than the instrumental noise. At the test station of SBB, this acceleration is still 50 times above the seismic noise level for the vertical component, but little above the seismic horizontal noise. The calibration system consists into a small telescope platform (diameter 0.5 m) supporting a horizontal bar of 1 m. Two metallic cylinders of equal mass (about 30 kg) are placed at the two ends of the bar, symmetrically with respect to the vertical rotation axis of the platform. The rotation velocity of the system is controlled with a high accuracy. The accelerometers are located at less than 1 m from the system axis. For the vertical component, we measured the sensitivity at various periods between 2000 and 50 sec, and the result was within 10 per cent of the specified sensitivity; this difference was of the same order as the expected accuracy. For the horizontal component, a slight asymmetry of the two masses with respect to the rotation center and an irregular coupling of the platform to the ground induced a periodic variation of the tilt, dominating over the gravitational signal of the masses at the frequencies of interest, which made the sensitivity measurement less accurate. Nevertheless, the result was still close to the announced sensitivity. We expect that an improved version of our calibration system will allow an accuracy of 1 per cent for the vertical, with a few hours of calibration. This will require an accuracy of a few millimeters in the geometry of the calibration system. Improving the results for the horizontal component will require a careful installation in order to eliminate the tilt perturbation and should lead to an accuracy of a few per cent.
Rupture history of the 1989 Loma Prieta, California, earthquake
Authors: Steidl Jamison H. , Archuleta Ralph J. , Hartzell Stephen H. 
Published: September 2021

AbstractStrong motion records of the 1989 Loma Prieta earthquake are inverted to determine a model of the rupture history. Uncorrected horizontal and vertical accelerograms are integrated to particle velocity time histories for 38 stations within an epicentral range of 75 km. The time histories are bandpassed filtered with corners at 0.05 and 1.0 Hz. These bandpassed time histories are inverted using a nonlinear method to solve for the distribution of slip amplitudes and rupture times at specified locations on the fault plane. The fault plane is specified a priori: 38 km long and 17 km wide, extending from 3 to 19 km depth at a constant dip of 70°. Starting models have rupture times based on constant rupture velocities of 2.5, 2.8, and 3.0 km/sec and uniform slip with rise times of 0.5, 1.0, 1.5, and 3.0 sec.The waveform inversion results show the strike-slip displacement is concentrated at the southern end of the rupture (rake = 156°) and the dip-slip displacement is concentrated at the northern end of the rupture (rake = 115°). The average total slip is partitioned almost equally between strike slip and dip slip (rake = 137°). The hypocentral area has an unusually small amount of slip with almost no slip in a region just to the north and up dip from the hypocenter. The rupture front is complex, propagating up dip to the south faster than it propagates to the north. The region of maximum strike slip to the southeast radiates simultaneously with the region of maximum dip slip to the northwest. The average rupture velocity is 3.0 km/sec, approximately 0.83 times the local shear wave speed. The calculated seismic moment is 3.5 ± 0.5 × 1026 dyne-cm.
Aftershock sequence of the 3 December 1988 Pasadena earthquake
Authors: Ma Kuo-Fong , Kanamori Hiroo 
Published: September 2021

Abstract
The Pasadena earthquake (ML = 4.9) of 3 December 1988 occurred at a depth of 16 km, probably on the Santa Monica - Raymond fault, which is recognized as one of the most important faults in the Los Angeles basin for its potential seismic hazard. Prior to this event, no earthquake larger than magnitude 4 had been recorded since 1930 in this area. High-quality seismograms were recorded with the Pasadena very broadband (VBB) system (IRIS-TERRAscope station) not only for the mainshock but also for the aftershocks at epicentral distances of 3 to 4 km. We determined the focal mechanisms of 9 aftershocks using these data; for most of the aftershocks, the first-motion data are too sparse to determine the mechanism. We combined the first-motion data and the waveform data of P, SV, and SH waves recorded with the VBB instrument to determine the mechanism and seismic moment of nine aftershocks. The average orientations of the P and T axes of the aftershocks are consistent with the strike of the Raymond fault. The ratio of the logarithm of cumulative seismic moment of aftershocks to that of the seismic moment of the mainshock is significantly smaller than commonly observed.
​Bibliometric Analysis of the Research Characteristics and Trends in Legume Mycorrhiza Field
Authors: Xu S.X. 
Published: September 2021

Background: Legumes are notable for wide distribution and indispensable food function. Majority of legume species are known to form mycorrhizal symbioses. The visualized and quantitative analysis legume mycorrhiza research has been reported although much attention has been paid in this field. Methods: This study reviewed and analyzed systematically the research characteristics and trends in legume mycorrhiza by bibliometric method based on the citation data collected from the Web of Science Core Collection by CiteSpace software. Result: The publication concerning legume mycorrhiza research increases rapidly and is still a hotspot. The most active collaboration countries are USA, France, Germany, China and Australia, whereas the two institutions of University of Western Australia and Chinese Academy of Sciences collaborate most with others. The intellectual structure analysis showed that the main intellectual base is nitrogen-fixing of cereal. The top ranked of keyword by bursts was rhizobia with strength value of 5.2899, which began from 2016 and ended in 2018. The distinction of 24 bursting keywords is relatively small, which showed that the research hotpot and trend should be interaction between legume plants and mycorrhizal fungi for improving nutrition absorption, N-fixation, resistance to stress and their mechanisms in future.
UAE's First End to End Standardized Workflow-Based Digital Transformation in a Giant Gas Producing Asset - Lessons Learned and Way Forward
Authors: Alsaeedi Ayesha Ahmed Abdulla Salem , Elabrashy Manar Maher Mohamed , Alzeyoudi Mohamed Ali , Albadi Mohamed Mubarak , Soni Sandeep , Isambertt Jose , Tripathi Deepak 
Published: September 2021

Abstract
The concept of integrated modeling and digital transformation has grown within the oil and gas industry over the past decade and every such digital transformation has its own set of challenges from which significant learnings can be derived to enhance the knowledge base of the industry. This paper encompasses the successful achievement journey from the UAE's first end to end standardized workflow- based digital transformation in a giant gas producing asset, where several key challenges and learnings have been summarized that are originated from a unique project for a giant gas-condensate asset.
The role and importance from multiple business stakeholders such as the planning, engineering, operations and performance teams was imperative to establish a collaborative working philosophy and a detailed specification document, the end-to-end solution, functional and non-functional requirements were captured and aligned with end-user needs.
Firstly, a detailed offline phase along with focused efforts in understanding data-quality and establishing representative base-models, was key to enhance the benefit-realization of the integrated platform. Secondly, the online implementation helped in achieving significant process efficiency improvement as inbuilt data validation features significantly improved the confidence of the output.
The diagnostic workflows replaced the conventional spreadsheet-based approach. The digital platform works as a common reference of "truth" for everyone across the organization. It helped to produce several the business KPIs to assist the engineers in emphasizing on the problem area, such as improved well test planning.
Numerical Study on the Temperature Behavior in Naturally Fractured Geothermal Reservoirs and Analysis Methodology for Geothermal Reservoir Characterization and Development
Authors: Wei Cao , Cheng Shiqing , Jiang Bin , Gao Ruilian , Wang Yang , Song Jiayi , Yu Haiyang 
Published: September 2021

Abstract
An important way to develop geothermal energy is by producing low-medium temperature fluids from naturally fractured geothermal reservoirs. Pressure analysis is the most used to characterize such reservoirs for improving development efficiency. However, pressure inversion easily leads to non-uniqueness and cannot estimate thermal properties. Additionally, no reliable methods are proposed to evaluate the development potential of geothermal reservoirs. To narrow the gap, this study aims at studying the temperature behaviors and exploring suitable analysis method for characterizing geothermal reservoir and evaluating development potential.
The numerical and analytical models are simultaneously established to analyze the temperature behaviors. Our models account for the J-T effect (μJT), adiabatic heat expansion/compression effect (η), reservoir damage, viscous dissipation, heat conduction and convection effects. The solution's development is dependent on the fact that the effects of reservoir temperature changes on transient pressure can be ignored so that the pressure and energy equations can be decoupled. We firstly compute reservoir pressure field based on Kazemi model, then use this obtained pressure field to solve the energy-balance equations. The numerical solution is verified and is found to be in good agreement with the proposed analytical solutions.
This work shows that the most used constant μJT and η assumption will produce inaccurate temperature results when reservoir temperature changes significantly. Moreover, we find that temperature behaviors can exhibit three heat radial flow regimes (HRFR) and a heat inter-porosity regime with V-shape characteristic. Fracture thermal storativity ratio and matrix heat inter-porosity coefficient defined in this study can be estimated from this characteristic, which are further used to evaluate geothermal development potential. Our work also shows that temperature data can give information that would not be provided by conventional pressure analysis. The temperature derivative curve will show ‘hump’ characteristic if reservoir is damaged. The temperature data can characterize the skin-zone radius and permeability. More than that, the properties such as J-T coefficient, effective adiabatic heat expansion coefficient and porosity can be estimated. Eventually, an integrated workflow of using both temperature and pressure data analysis is presented to characterize naturally fractured geothermal reservoir for the first time. Simulated test examples were interpreted to demonstrate its applicability.
Application of Interventionless Single Point Entry Technology to Improve Proppant Placement Control and Well Production
Authors: Griffin J. , Rojas D. J. , Al Shmakhy A. , Scranton P. 
Published: September 2021

Abstract
The hydraulic fracture treatment (HFT) and its effectiveness to enhance wellbore drainage directly correlate with each well’s overall production performance and underlining economics. This paper will discuss the potential of ultra high stage count Single Point Entry (SPE) sleeves and their ability to increase control over proppant placement and isolation during the HFT as a method for optimizing well performance, economics, and reduce non-uniformity between treatments and wells.
To address the limitations of current completion methods, full ID single point entry systems have been developed for open hole and cemented applications. These systems provide unlimited frac stage count with lower frac tortuosity, provide increased control over proppant placement and well production, reduce or eliminate over- flush and formation damage, and achieve higher efficiency during and after frac stimulation than previous conventional plug-and-perf (PnP) and sleeve systems, thereby reducing costs.
While the ball-and-seat completion technique revolutionized the efficiency of multi-stage single point entry fracturing, its vast array of limitations (primarily ID restrictions), limited stage count, and compatibility with cemented liners quickly sidelined it in place of PnP. PnP offers increased surface area contact through additional entry points compared to sleeve systems of the past and remains the accepted method for achieving zonal isolation and initiation during stimulation. However, the time intensive operations of PnP present challenges in maintaining efficiencies due to variability in wireline during deployment and coiled tubing during millouts. The increase in number of clusters per stage and number of stages per well achieved with PnP often results in higher stimulated rock volumes (SRV) however, due to the number of multiple clusters open simultaneously, this method gained a "pump-n-pray" reputation due to the uncertainty of cluster efficiency and its unpredictability. The lack of cluster control over the years has created a series of challenges in terms of parent-child well relationships and spacing, economical asset development, and loss of potential production.
With over 4,000 stages fracture stimulated across US, Canada, and Asia, some wells containing 220 individual stages, this paper will address the differences in production in terms of bbl of oil equivalent (BOE) for direct and indirect offsets in trials, compare capital efficiency with spud to put on production (POP) timelines, demonstrate economical completion optimization for lower commodity pricing of oil, and carbon intensity reduction measures to lower greenhouse gas emissions.