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At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Capabilities of multivariate Bayesian inference toward seismic hazard assessment

Multivariate Bayesian analysis can bring significant benefits to seismic hazard analysis: Its multivariate feature enables computing scalar and vector hazard without making any approximations; Correlations between intensity measures are implicitly modeled, permitting direct simulation of ground motion selection tools such as the conditional mean spectrum and the generalized conditioning intensity measure; and Its updating feature enables a seamless integration of new ground motion data into the hazard results. Here, we first develop a multivariate Bayesian ground motion model through the NGA-West2 database. The model functional form considers fault-type, magnitude, and distance dependencies, and also the linear and the rock intensity dependent site response. We use a hybrid Markov Chain Monte Carlo sampling to perform Bayesian inference consisting of Gibbs step and a multilevel Metropolis-Hastings step. We then perform several checks on the model and note that its performance is satisfactory. Finally, we illustrate the merits of this multivariate Bayesian analysis, which include: ground motion model updating with ground motion data recorded in the last four years not part of the NGA-West2 database; computation of scalar and vector seismic hazard using the un-updated and updated ground motion models for Los Angeles, CA; and simulation of the conditional mean spectrum under scalar and vector IM conditioning while accounting for different sources of aleatoric and epistemic uncertainties.

58 GEOSCIENCES↗
DOE OSTI2017

Simulations of Seismic Wave Propagation on Mars

In this paper, we present global and regional synthetic seismograms computed for 1D and 3D Mars models based on the spectral-element method. For global simulations, we implemented a radially-symmetric Mars model with a 110 km thick crust. For this 1D model, we successfully benchmarked the 3D seismic wave propagation solver SPECFEM3D_GLOBE against the 2D axisymmetric wave propagation solver AxiSEM at periods down to 10 s. We also present higher-resolution body-wave simulations with AxiSEM down to 1 s in a model with a more complex 1D crust, revealing wave propagation effects that would have been difficult to interpret based on ray theory. For 3D global simulations based on SPECFEM3D_GLOBE, we superimposed 3D crustal thickness variations capturing the distinct crustal dichotomy between Mars’ northern and southern hemispheres, as well as topography, ellipticity, gravity, and rotation. The global simulations clearly indicate that the 3D crust speeds up body waves compared to the reference 1D model, whereas it significantly changes surface waveforms and their dispersive character depending on its thickness. We also perform regional simulations with the solver SES3D based on 3D crustal models derived from surface composition, thereby addressing the effects of various distinct crustal features down to 2 s. The regional simulations confirm the strong effects of crustal variations on waveforms. Finally, we conclude that the numerical tools are ready for examining more scenarios, including various other seismic models and sources.

58 GEOSCIENCES↗
DOE OSTI2020

Seismic identification of geothermal prospecting in Harrat Rahat, Northern Arabian Shield

Harrat Rahat volcanic field lies along the Makkah-Madinah-Nafud active volcanic line. It has extensive linear weak zones of wrench faults that could provide ideal conduits for upwelling magma and hydrothermal fluids as well. Here, passive seismic data recorded by seismic stations installed within and around Harrat Rahat has been processed for the detection of microseismic events. Moreover, ambient noise was also gathered and analyzed to construct a subsurface velocity model. This model indicates low velocity zone in Harrat Rahat, and two areas with coincident basement faults and possibly with enhanced subsurface temperatures were identified. It is concluded that Harrat Rahat has high geothermal potential and promising for geothermal renewable power.

58 GEOSCIENCES↗
DOE OSTI2020

Seismic monitoring and high-frequency noise using arrays in the Arabian Peninsula

Seismic arrays provide useful tools for regional seismic monitoring. Two small-aperture, regionally-oriented arrays, QWAR and HQAR, were deployed in Saudi Arabia and Oman in 2012 and 2016. We utilize a time-domain beampacking method, similar to frequency-wavenumber analysis, to examine the performance of the arrays in terms of slowness and azimuthal bias and event detection capabilities. Additionally, we investigate persistent ambient noise sources recorded by the arrays. We find that the arrays provide slowness vectors with biases comparable with similar-sized arrays of the International Monitoring System in other locations around the world. At QWAR, regional events of magnitude 3.0 and above are detected a majority of the time, and as magnitudes increase to 4.0 and above, the detection rate is greater than 82%. Finally, strong noise generation, primarily with slownesses characteristic of Lg waves, is found in the directions of the northern Arabian/Persian Gulf and southern Red Sea and may be a factor in event detection capabilities.

58 GEOSCIENCES↗
DOE OSTI2026

3D seismic imaging of a fracture damage zone controlling reservoir compartmentalization at the Raft River EGS using multi-azimuth walkaway VSP

Accurate imaging of steeply dipping fracture zones in crystalline enhanced geothermal systems (EGS) is critical for constraining permeability architecture and guiding stimulation design. However, such structures remain poorly resolved by conventional surface seismic methods. We present a fully three-dimensional (3D) elastic-waveform inversion-migration workflow applied to multi-azimuth walkaway vertical seismic profiling (VSP) data acquired in a deviated borehole at the Raft River EGS. The workflow integrates first-arrival traveltime tomography, multi-scale elastic waveform inversion (EWI), and elastic least-squares reverse-time migration (ELSRTM) to recover high-resolution compressional-and shear-wave velocity models and to image structural discontinuities in the crystalline basement. The results reveal a laterally continuous low-velocity anomaly, with shear-wave velocity reductions of 25-30%, consistent with fractureinduced mechanical weakening. Two steeply dipping discontinuities bound a 50-80 m wide fracture damage zone. Independent constraints from microseismic clustering and geochemical compartmentalization corroborate the geometry and structural significance of this feature. Synthetic modeling further confirms that structures of this scale are resolvable (~30 m). These findings indicate that the Narrows structure is a distributed fracture damage zone rather than a discrete fault plane. By resolving fracture-zone geometry at the tens-of-meters scale using a single borehole, this workflow provides a practical and transferable approach for improving structural characterization, reducing uncertainty in permeability architecture, and supporting reservoir modeling and stimulation design in fractured crystalline EGS reservoirs.

58 GEOSCIENCES↗
DOE OSTI2017

Electrical and seismic response of saline permafrost soil during freeze - Thaw transition

We conducted laboratory studies on the geophysical signals from Arctic saline permafrost soils to help understand the physical and mechanical processes during freeze-thaw cycles. Our results revealed low electrical resistivity (< 20 Ωm) and elastic moduli (7.7 GPa for Young's modulus and 2.9 GPa for shear modulus) at temperatures down to ~- 10 °C, indicating the presence of a significant amount of unfrozen saline water under the current field conditions. The spectral induced polarization signal showed a systematic shift during the freezing process, affected by concurrent changes of temperature, salinity, and ice formation. An anomalous induced polarization response was first observed during the transient period of supercooling and the onset of ice nucleation. Seismic measurements showed a characteristic maximal attenuation at the temperatures immediately below the freezing point, followed by a decrease with decreasing temperature. The calculated elastic moduli showed a non-hysteric response during the freeze – thaw cycle, which was different from the concurrently measured electrical resistivity response where a differential resistivity signal is observed depending on whether the soil is experiencing freezing or thawing. The differential electrical resistivity signal presents challenges for unfrozen water content estimation based on Archie's law. Using an improved formulation of Archie's law with a variable cementation exponent, the unfrozen water content estimation showed a large variation depending on the choice of the resistivity data during either a freezing or thawing cycle. Combining the electrical and seismic results, we suggest that, rather than a large hysteresis in the actual unfrozen water content, the shift of the resistivity response may reflect the changes of the distribution pattern of the unfrozen water (or ice) in the soil matrix during repeated freeze and thaw processes. Collectively, our results provide an improved petrophysical understanding of the physical and mechanical properties of saline permafrost during freeze – thaw transitions, and suggest that large uncertainty may exist when estimating the unfrozen water content using electrical resistivity data.

58 GEOSCIENCES↗
DOE OSTI2022

Potential Seismicity Along Basement Faults Induced by Geological Carbon Sequestration

Large-scale CO 2 sequestration into geological formations has been suggested to reduce CO 2 emissions from industrial activities. However, much like enhanced geothermal stimulation and wastewater injection, CO 2 sequestration has a potential to induce earthquake along weak faults, which can be considered a negative impact on safety and public opinion. This research shows the physical mechanisms of potential seismic hazards along basement faults driven by CO 2 sequestration under variation in geological and operational constraints. Specifically we compare the poroelastic behaviors between multiphase flow and single-phase flow cases, highlighting specific needs of evaluating induced seismicity associated with CO 2 sequestration. In contrast to single-phase injection scenario, slower migration of the CO 2 plume than pressure pulse may delay accumulation of pressure and stress along basement faults that may not be mitigated immediately by shut-in of injection. The impact of multiphase flow system, therefore, needs to be considered for proper monitoring and mitigation strategies.

58 GEOSCIENCES↗
DOE OSTI2023

Understanding Subsurface Fracture Evolution Dynamics Using Time‐Lapse Full Waveform Inversion of Continuous Active‐Source Seismic Monitoring Data

Abstract Predicting the behavior, geometry, and flow properties of subsurface fractures remains a challenging problem. Seismic models that can characterize fractures usually suffer from low spatiotemporal resolution. Here, we develop a correlative double‐difference time‐lapse full waveform inversion of continuous active source seismic monitoring data for determining high‐spatiotemporal‐resolution time‐lapse V p models of in‐situ fracture evolution at a shallow contamination site in Wyoming, USA. Assisted by rock physics modeling, we find that (a) rapidly increasing pore pressure initializes and grows the fracture, increasing the porosity slightly (from ∼13.7% to ∼14.6%) in the tight clay formation, thus decreasing V p (∼50 m/s); (b) the fluid injection continues decreasing V p , likely through the introduction of gas bubbles in the injectate; and (c) final V p reductions reach over ∼150 m/s due to a posited ∼4.5% gas saturation. Our results demonstrate that high‐resolution V p changes are indicative of mechanical and fluid changes within the fracture zone during hydrofracturing.

58 GEOSCIENCES↗
DOE OSTI2012

Note: Rotaphone, a new self-calibrated six-degree-of-freedom seismic sensor

We have developed and tested (calibration, linearity, and cross-axis errors) a new six-degree-of-freedom mechanical seismic sensor for collocated measurements of three translational and three rotational ground motion velocity components. The device consists of standard geophones arranged in parallel pairs to detect spatial gradients. The instrument operates in a high-frequency range (above the natural frequency of the geophones, 4.5 Hz). Its theoretical sensitivity limit in this range is 10{sup -9} m/s in ground velocity and 10{sup -9} rad/s in rotation rate. Small size and weight, and easy installation and maintenance make the instrument useful for local-earthquake recording and seismic prospecting.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

Polarized seismic and solitary waves run-up at the sea bed

The polarization effects in hydrodynamics are studied. Hydrodynamic equation for the nonlinear wave is used along with the polarized solitary waves and seismic waves act as initial waves. The model is then solved by Fourier spectral and Runge-Kutta 4 methods, and the surface plot is drawn. The output demonstrates the inundation behaviors. Consequently, the polarized seismic waves along with the polarized solitary waves tend to generate dissimilar inundation which is more disastrous.

58 GEOSCIENCES↗
DOE OSTI2013

Study of seismicity around Toba area based on relocation hypocenter result from BMKG catalogue

Toba area has complex tectonic setting attracting many earth scientists to study and understand tectonic and geological process or setting. The area is affected by oblique subduction zone, Renun Sumatran fault sub segment and some volcanoes that are near it. The earthquake catalogue provided by BMKG from April, 2009 to December, 2011 must be relocated firstly to get the precise hypocenter. We used catalogue data of P and S phase or P phase only and double-difference method to relocate the earthquakes. The results show hypocenter position enhancement that can be interpreted tectonically. The earthquakes after relocation relating to the Sumatran fault, subduction zone, volcanoes and seismic activities beneath Toba caldera can be mapped clearly. The relocated hypocenters in this study are very important to provide information for seismic hazard assessment and disaster mitigation study.

58 GEOSCIENCES↗
DOE OSTI2014

Numerical simulation of tectonic plates motion and seismic process in Central Asia

An evolutionary approach proposed in [1, 2] combining the achievements of traditional macroscopic theory of solid mechanics and basic ideas of nonlinear dynamics is applied in a numerical simulation of present-day tectonic plates motion and seismic process in Central Asia. Relative values of strength parameters of rigid blocks with respect to the soft zones were characterized by the δ parameter that was varied in the numerical experiments within δ = 1.1–1.8 for different groups of the zonal-block divisibility. In general, the numerical simulations of tectonic block motion and accompanying seismic process in the model geomedium indicate that the numerical solutions of the solid mechanics equations characterize its deformation as a typical behavior of a nonlinear dynamic system under conditions of self-organized criticality.

58 GEOSCIENCES↗
DOE OSTI2015

The preliminary results: Internal seismic velocity structure imaging beneath Mount Lokon

Historical records that before the 17{sup th} century, Mount Lokon had been dormant for approximately 400 years. In the years between 1350 and 1400, eruption ever recorded in Empung, came from Mount Lokon’s central crater. Subsequently, in 1750 to 1800, Mount Lokon continued to erupt again and caused soil damage and fall victim. After 1949, Mount Lokon dramatically increased in its frequency: the eruption interval varies between 1 – 5 years, with an average interval of 3 years and a rest interval ranged from 8 – 64 years. Then, on June 26{sup th}, 2011, standby alert set by the Center for Volcanology and Geological Hazard Mitigation. Peak activity happened on July 4{sup th}, 2011 that Mount Lokon erupted continuously until August 28{sup th}, 2011. In this study, we carefully analyzed micro-earthquakes waveform and determined hypocenter location of those events. We then conducted travel time seismic tomographic inversion using SIMULPS12 method to detemine Vp, Vs and Vp/Vs ratio structures beneath Lokon volcano in order to enhance our subsurface geological structure. During the tomographic inversion, we started from 1-D seismic velocities model obtained from VELEST33 method. Our preliminary results show low Vp, low Vs, and high Vp/Vs are observed beneath Mount Lokon-Empung which are may be associated with weak zone or hot material zones. However, in this study we used few station for recording of micro-earthquake events. So, we suggest in the future tomography study, the adding of some seismometers in order to improve ray coverage in the region is profoundly justified.

58 GEOSCIENCES↗
DOE OSTI2015

On the possible relations between solar activities and global seismicity in the solar cycle 20 to 23

Solar activities consist of high energetic particle streams, electromagnetic radiation, magnetic and orbital gravitational forces. The well-know solar activity main indicator is the existence of sunspot which has mean variation in 11 years, named by solar cycle, allow for the above fluctuations. Solar activities are also related to the space weather affecting all planetary atmospheric variability, moreover to the Earth’s climate variability. Large extreme space and geophysical events (high magnitude earthquakes, explosive volcanic eruptions, magnetic storms, etc.) are hazards for humankind, infrastructure, economies, technology and the activities of civilization. With a growing world population, and with modern reliance on delicate technological systems, human society is becoming increasingly vulnerable to natural hazardous events. The big question arises to the relation between solar forcing energy to the Earth’s global seismic activities. Estimates are needed for the long term occurrence-rate probabilities of these extreme natural hazardous events. We studied connectivity from yearly seismic activities that refer to and sunspot number within the solar cycle 20 to 23 of year 1960 to 2013 (53 years). We found clear evidences that in general high magnitude earthquake events and their depth were related to the low solar activity.

58 GEOSCIENCES↗
DOE OSTI2015

Searching for the corner seismic moment in worldwide data

In this paper the existence of the corner frequency value for the seismic moment distribution is investigated, analysing worldwide data. Pareto based distributions, usually considered as the most suitable to this type of data, are fitted to the most recent data, available in a global earthquake catalog. Despite the undeniable finite nature of the seismic moment data, we conclude that no corner frequency can be established considering the available data set.

58 GEOSCIENCES↗
DOE OSTI2021

Widespread deep seismicity in the Delaware Basin, Texas, is mainly driven by shallow wastewater injection

Significance The Delaware Basin, western Texas, has experienced a surge in the number of earthquakes. We investigate basin-wide earthquake, hydrogeologic, industrial, and geodetic data spanning 1993–2020 to identify the reasons for the increase. We use these data and models to quantify the stress changes from wastewater injection and hydrocarbon extraction. We demonstrate that the basin-wide seismicity is dominated by the stresses caused by shallow injection that are transmitted vertically by deforming the underlying crust. We analyze both injection and production data to understand how subsurface properties control earthquake locations and timings. We suggest that injecting wastewater into porous formations will minimize seismic hazard. We establish a framework explaining why earthquakes sometimes occur and sometimes do not occur within human activity-impacted areas.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2011

COMPARISON OF SEISMIC SIGNATURES OF FLARES OBTAINED BY SOHO/MICHELSON DOPPLER IMAGER AND GONG INSTRUMENTS

The first observations of seismic responses to solar flares were carried out using time-distance (TD) and holography techniques applied to SOHO/Michelson Doppler Imager (MDI) Dopplergrams obtained from space and unaffected by terrestrial atmospheric disturbances. However, the ground-based network GONG is potentially a very valuable source of sunquake observations, especially in cases where space observations are unavailable. In this paper, we present an updated technique for pre-processing of GONG observations for the application of subjacent vantage holography. Using this method and TD diagrams, we investigate several sunquakes observed in association with M- and X-class solar flares and compare the outcomes with those reported earlier using MDI data. In both GONG and MDI data sets, for the first time, we also detect the TD ridge associated with the 2001 September 9 flare. Our results show reassuringly positive identification of sunquakes from GONG data that can provide further information about the physics of seismic processes associated with solar flares.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

PROPAGATION OF SEISMIC WAVES THROUGH A SPATIO-TEMPORALLY FLUCTUATING MEDIUM: HOMOGENIZATION

Measurements of seismic wave travel times at the photosphere of the Sun have enabled inferences of its interior structure and dynamics. In interpreting these measurements, the simplifying assumption that waves propagate through a temporally stationary medium is almost universally invoked. However, the Sun is in a constant state of evolution, on a broad range of spatio-temporal scales. At the zero-wavelength limit, i.e., when the wavelength is much shorter than the scale over which the medium varies, the WKBJ (ray) approximation may be applied. Here, we address the other asymptotic end of the spectrum, the infinite-wavelength limit, using the technique of homogenization. We apply homogenization to scenarios where waves are propagating through rapidly varying media (spatially and temporally), and derive effective models for the media. One consequence is that a scalar sound speed becomes a tensorial wave speed in the effective model and anisotropies can be induced depending on the nature of the perturbation. The second term in this asymptotic two-scale expansion, the so-called corrector, contains contributions due to higher-order scattering, leading to the decoherence of the wave field. This decoherence may be causally linked to the observed wave attenuation in the Sun. Although the examples we consider here consist of periodic arrays of perturbations to the background, homogenization may be extended to ergodic and stationary random media. This method may have broad implications for the manner in which we interpret seismic measurements in the Sun and for modeling the effects of granulation on the scattering of waves and distortion of normal-mode eigenfunctions.

79 ASTRONOMY AND ASTROPHYSICS↗