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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Shallow Crustal Structure and Site Response at Fort Greely, Alaska

Fort Greely, Alaska is located in proximity to numerous faults capable of generating large (MW > 6.5) and damaging earthquakes. However, little knowledge exists about the noise properties, shallow crustal structure and site response of the area. We address this by examining ambient noise conditions, Rayleigh wave group wavespeed dispersion, and site response measurements using new and existing seismic data from December 2020 – April 2021 for four sites along a north-south line—stations GREN, GRES, PS09, K24K operated by the Alaska Earthquake Center. We find that ambient noise levels are relatively high on base compared to other places in Central Alaska, especially above 1 Hz, while noise levels in the microseismic band are typical of the region. Short-period (0.5 – 2Hz) Rayleigh wave group wavespeeds appear to decrease with increasing sediment thickness and increase when going southward from GREN to K24K. The predominant site frequency related to sediment thickness is lowest beneath PS09 and highest beneath K24K. We use the group velocities and site response values to propose a rough north-south layered model for the region.

58 GEOSCIENCES↗
DOE OSTI2020

Crustal Structure of the Mesopotamian Plain, East of Iraq

The crustal structure of Iraq was investigated through analyzing teleseismic data from 12 new seismic stations. Three seismic stations are located within the Zagros Fold-Thrust Belt, and nine are within the Mesopotamian Plain. Joint inversion of P wave receiver function and Rayleigh wave dispersion data were employed to resolve S wave velocity structure models beneath each station. Combining these models with available Moho depths within and around the study area reveals that the Moho depth is smoothly increasing from the Arabian platform toward the Zagros Mountains. Further, an exceptional deeper root is observed near the eastern edge of the Mesopotamian Plain where sedimentary pile is the thickest. This root was interpreted as a structure inherited from the successive Mesozoic rifting of the NE Arabian platform enhanced by sedimentary loading and progressive subsidence. A low-velocity uppermost mantle was observed beneath the Arabian Foredeep attesting the existence of a low-strength lithospheric mantle beneath the region southwest from the Zagros deformation front. The weak rheology of the uppermost mantle may have allowed local sinking of the crust and deepening of the Moho boundary due to vertical loading and the Late Miocene lateral contraction.

58 GEOSCIENCES↗
NASA NTRS1984

Aspherical heterogeneity of the mantle from phase velocities of mantle waves

Long-period surface waves are used to map the lateral heterogeneity of the upper 100-600 km of the mantle. There is good correlation of velocity with surface tectonics and heat flow. Convergence regions are generally slow for Love waves and fast for Rayleigh waves. Back arc basins have slower than average shallow mantle. Some island arcs show evidence of fast material at greater depth. Deep-seated slow anomalies underlie the Red Sea-Afar region of north-east Africa, western North American-northern East Pacific Rise, Indian Ocean triple junction and the Tasman Sea-Campbell Plateau regions. The fastest regions are in the north central Australia-New Guinea and the South Atlantic.

Nakanishi, I.↗
DOE OSTI2023

Crustal and uppermost mantle structure near the Gloria Fault, North Atlantic, from ocean bottom seismometer surface wave observations

SUMMARY In this work, we present both 1-D and 3-D shear wave velocity (Vs) models of the oceanic crust and uppermost mantle below the Deep OCean Test ARray area, located ∼ 70 km north of the central section of the Gloria Fault, in the eastern North-Atlantic Ocean. The velocity models are inferred from the dispersion of surface waves recorded on ocean bottom seismometers. Dispersion measurements are obtained from the analysis of ambient seismic noise at short periods (< 14 s) and teleseismic surface waves at long periods (> 14 s) using the two-station method. The 1-D Vs model is inferred from the joint inversion of Rayleigh wave phase velocities and Love wave group and phase velocities. The 3-D tomographic model is obtained by inversion of 2-D Love wave group velocity maps as a function of depth, further constrained by the average of Love wave phase velocities obtained from ambient noise (4–9 s) and the average Rayleigh and Love wave phase velocities calculated from teleseismic data (14–44 s). The 1-D Vs model shows a sediment layer with a low velocity of 1.05 km s−1, similar to previous studies in the region. Below the sediments, we find an oceanic crust with velocities ranging from 3.3 to 4.5 km s−1. The model reaches an unusually high velocity of 4.9 km s−1 in a 20 km thick layer at depths between 16 and 36 km. We interpret this fast velocity layer as indicative of the presence of harzburgite, a residue of enhanced melting that might have been formed by the proximity between the Mid-Atlantic Ridge and the Azores mantle plume. At greater depths the velocity decreases, forming a low-velocity zone that reaches a minimum at ∼ 70 km depth, which we interpret as the maximum depth for the lithosphere–asthenosphere boundary. The 3-D model shows a structure that is mostly horizontally layered, with Vs isocontours at 3.5–4.5 km s−1 highlighting oscillations of the crustal structure with wavelengths of ∼25–30 km. These oscillations may be due to changes in the rate of mantle upwelling and magma supply rate.

Pinzón, Juan I. (ORCID:0000000338078068)↗
NASA NTRS1975

A surface-wave investigation of the rupture mechanism of the Gobi-Altai (4 December 1957) earthquake

Long period records of multiple Love waves from the 1957 earthquake in Mongolia at Pasadena are analyzed and compared to synthetic seismograms, generated by the method of Kanamori. A fit in the time domain shows that the records are not consistent with the previous solution, achieved through a frequency domain analysis of directivity. The solution asks for a shorter rupture of 270 km at a velocity of 3.5 km/s. The focal parameters are constrained by updating all the reported first motion and are found to be: Strike = 103 deg, Dip = 53 deg, Slip = 32 deg. A seismic moment of 1.8 10 to the 28th power dynes-cm is obtained. These figures are also consistent with a time domain analysis of Love waves at Palisades and Strasbourg, and of Rayleigh waves at Pasadena, with a directivity study of Love waves at Pasadena, and with static deformation and isoseismal data. A discussion is given of the relation between moment, magnitude and rupture area, and a comparison is made with other events in the same region: It is concluded that this earthquake does not exhibit an intra-plate behavior, but rather compares better with inter-plate events, such as the great Assam earthquake.

Okal, E. A.↗
DOE OSTI2021

Data–Driven Velocity Model Evaluation Using K–Means Clustering

In this work, we develop a data-driven clustering method to evaluate a velocity model using surface wave velocity dispersion. This is done by first computing theoretical dispersion curves for 1-D velocity profiles of all the grid locations and then splitting the resulting dispersion curves into a certain number of groups via the K-means clustering. The observed dispersion curves are also clustered following the same procedure and the velocity model is assessed by comparing the spatial patterns obtained for the observed and synthetic data sets. The method is applied to evaluate two community velocity models in southern California, CVM-S4.26 and CVM-H15.1, using phase velocity maps derived for 3–16 s Rayleigh waves. We found a good correlation in the spatial distribution of clusters between the result of CVM-S4.26 and that of the observed data, suggesting that the CVM-S4.26 fits the observed dispersion maps better than the CVM-H15.1 in terms of features extracted from the clustering analysis.

58 GEOSCIENCES↗
DOE OSTI2022

In situ detection and characterization of alkali-silica reaction damage in concrete using contactless ultrasonic wavefield imaging

Here we present work to characterize cracking damage in concrete caused by alkali-silica reactivity distress. We apply contactless ultrasonic scan inspection, exploiting Rayleigh wave scattering from concrete inhomogeneities. The scanning system utilizes a multi-channel MEMS sensor array to collect ultrasonic wavefield data from concrete subjected to ASR-promoting environments. The location and extent of ASR damage are established by internal expansion measurements from embedded strain gauges, scanning electron microscope images of cored samples, and expansion measurements from companion samples. A wavefield data processing method extracts oscillatory fields from the ultrasonic wavefield data to detect distinct zones of ASR damage. A damage index is proposed to further characterize the extent of ASR damage. The results confirm the feasibility and accuracy of the approach to characterize ASR damage in concrete. The fully contactless ultrasonic scanning measurement system does not require separate material samples and enables in situ characterization of ASR damage within concrete structures.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Sensitivity measurements for a 250 MHz quartz shear-horizontal surface acoustic wave biosensor under liquid viscous loading

Surface acoustic wave (SAW) devices have been used in biochemical assays due to their high sensitivity. The device sensitivity is a function of changes in the density and viscosity of the liquid. Here, we studied the effect of fluid viscosity using a 250 MHz quartz shear-horizontal (SH)-SAW biosensor by monitoring different concentrations of binary aqueous/glycerol solutions. In this study, the sensitivity of the biosensor was determined by fitting the data to models derived from perturbation theory. Measurements in water were used as the reference. For a 0% to 50% glycerol solution, an 87°–204° separation in the phase shift was observed. The slope of the plot of the phase shift vs (ηρ)0.5 was used to indicate the sensor’s sensitivity. The sensitivity for our 250 MHz quartz SH-SAW sensors was calculated to be 3.7×10−3m2sKg. The corresponding mass sensitivity was determined to be 9.25 × 105m2Kg. The limit of detection was calculated to be 36 picograms (pg), while the limit of quantification or LOQ was calculated to be 109 pg. Traditionally, liquid phase measurements have been challenging for SAW devices because liquids dampen the vibrating sensors severely. This problem has been largely solved using a transverse (shear) wave instead of the more popular longitudinal or Rayleigh waves. Liquid measurements are now possible using transverse waves, also known as shear waves, because transverse waves are only minimally attenuated by liquids. Shear-horizontal SAW sensors (SH-SAW) show great promise as label-free biosensors because of their ability to handle liquid samples. However, the viscosity of the liquid still induces loading effects and can be measured when the liquid is loaded onto the SH-SAW propagating surface (delay line). When the liquid above the delay line is perturbed by physical or chemical changes, such as binding to a receptor, it alters the propagating acoustic wave. The SH-SAW device can measure these changes in liquid properties as a change in the wave’s phase compared to the original wave. The device’s phase shift was recorded as a function of the changes in the density and viscosity of the binary glycerol solution and used to determine the sensitivity in the linear dynamic range of responses.

Materials Science↗
NASA NTRS1984

Surface wave tomography

Vertically polarized shear wave velocity (VSV), determined primarily from fundamental mode Rayleigh waves, and the difference between the velocity of horizontally polarized shear waves (VSH) and VSV, therefore a measure of anisotropy, are shown.

Anderson, D. L.↗
NASA NTRS1984

Surface wave tomography

Vertically polarized shear wave velocity (VSV), determined primarily from fundamental mode Rayleigh waves, and the difference between the velocity of horizontally polarized shear waves (VSH) and VSV, therefore a measure of anisotropy, are shown. Previously announced in STAR as N84-17728

Anderson, D. L.↗
DOE OSTI2025

STILGAR: Subsurface Models for Graymont Pleasant Gap Mine

The detection, location, and monitoring of underground structures are of great importance to national and global security. Tunnels and voids generate seismic signatures detectable at the surface, but using non-invasive seismic data to image near-surface presents several challenges in real-world applications. In this report, we describe the use of a dense surface seismic deployment to generate subsurface models of the Graymont Pleasant Gap mine - a single-layer mine with a complex structure embedded in a high-velocity P-wave limestone bedrock. Our approach consists of three key methods. We use P-wave arrival times from local blast events to perform a tomography inversion with the tomoTD method, constructing a P-wave velocity model of the subsurface. We model the layer above the mine using Rayleigh wave ellipticity and inversion techniques. We leverage ongoing anthropogenic activities to identify and locate noise sources both on the surface and within the subsurface. With this integrated approach we aim to overcome the challenges and enhance our ability to non-invasively characterize underground structures, contributing to improved seismic monitoring techniques.

58 GEOSCIENCES↗
DOE OSTI2021

Profiling the Quito basin (Ecuador) using seismic ambient noise

SUMMARY Quito, the capital of Ecuador, with more than 2.5 M inhabitants, is exposed to a high seismic hazard due to its proximity to the Pacific subduction zone and active crustal faults, both capable of generating significant earthquakes. Furthermore, the city is located in an intermontane piggy-back basin prone to seismic wave amplification. To understand the basin’s seismic response and characterize its geological structure, 20 broad and medium frequency band seismic stations were deployed in Quito’s urban area between May 2016 and July 2018 that continuously recorded ambient seismic noise. We first compute horizontal-to-vertical spectral ratios to determine the resonant frequency distribution in the entire basin. Secondly, we cross-correlate seismic stations operating simultaneously to retrieve interstations surface-wave Green’s functions in the frequency range of 0.1–2 Hz. We find that Love waves travelling in the basin’s longitudinal direction (NNE–SSW) show much clearer correlograms than those from Rayleigh waves. We then compute Love wave phase-velocity dispersion curves and invert them in conjunction with the HVSR curves to obtain shear-wave velocity profiles throughout the city. The inversions highlight a clear difference in the basin’s structure between its northern and southern parts. In the centre and northern areas, the estimated basin depth and mean shear-wave velocity are about 200 m and 1800 ms−1, respectively, showing resonance frequency values between 0.6 and 0.7 Hz. On the contrary, the basement’s depth and shear-wave velocity in the southern part are about 900 m and 2500 ms−1, having a low resonance frequency value of around 0.3 Hz. This difference in structure between the centre-north and the south of the basin explains the spatial distribution of low-frequency seismic amplifications observed during the Mw 7.8 Pedernales earthquake in April 2016 in Quito.

Pacheco, D. (ORCID:0000000282355096)↗
NASA NTRS1991

Singularities in water waves and Rayleigh-Taylor instability

Singularities in inviscid two-dimensional finite-amplitude water waves and inviscid Rayleigh-Taylor instability are discussed. For the deep water gravity waves of permanent form, through a combination of analytical and numerical methods, results describing the precise form, number, and location of singularities in the unphysical domain as the wave height is increased are presented. It is shown how the information on the singularity in the unphysical region has the same form as for deep water waves. However, associated with such a singularity is a series of image singularities at increasing distances from the physical plane with possibly different behavior. Furthermore, for the Rayleigh-Taylor problem of motion of fluid over a vacuum and for the unsteady water wave problem, integro-differential equations valid in the unphysical region are derived, and how these equations can give information on the nature of singularities for arbitrary initial conditions is shown.

Tanveer, S.↗
NASA NTRS1991

Singularities in water waves and Rayleigh-Taylor instability

Singularities in inviscid two-dimensional finite-amplitude water waves and inviscid Rayleigh-Taylor instability are discussed. For the deep water gravity waves of permanent form, through a combination of analytical and numerical methods, results describing the precise form, number, and location of singularities in the unphysical domain as the wave height is increased are presented. It is shown how the information on the singularity in the unphysical region has the same form as for deep water waves. However, associated with such a singularity is a series of image singularities at increasing distances from the physical plane with possibly different behavior. Furthermore, for the Rayleigh-Taylor problem of motion of fluid over a vacuum and for the unsteady water wave problem, integro-differential equations valid in the unphysical region are derived, and how these equations can give information on the nature of singularities for arbitrary initial conditions is shown.

Tanveer, S.↗
DOE OSTI2025

Structure of the Ecuadorian Upper Plate From a Joint Seismic‐Gravity Inversion

The Ecuadorian portion of the South American subduction zone presents an interesting case study in the structure and complex evolution of an upper plate. There are outstanding questions about its tectonic history, composition, and magmatic processes. While previous studies have employed ambient noise tomography to image the Ecuadorian upper plate, surface wave inversions alone often lack sensitivity at relevant shallow depths. This limitation can be overcome with an independent, complementary data set, such as gravity. We have jointly inverted Rayleigh wave phase velocities and Bouguer gravity anomalies to provide a more detailed seismic velocity model of the Ecuadorian upper plate. Our joint inversion has yielded several key improvements from previous models. First, we observe much shallower slow velocities beneath major basins (the Manabí, Progreso, and Gulf of Guayaquil), better aligning with expected basin structure. Second, we identify a high-velocity block beneath the entire forearc, corresponding to the Piñon Terrane, with velocities suggesting the presence of ultramafic material. Third, we highlight a new narrow swath of slow velocities beneath the Ecuadorian Andes, which closely follows the active volcanoes along the Eastern Cordillera. The extent of these slow velocities coincides with the termination of active arc volcanism and the predicted location of the subducted Carnegie Ridge. The predicted compositions for the mid to lower crust in the region preclude a purely compositional explanation for these velocities, suggesting that some level of partial melt is necessary.

Birkey, Andrew [Univ. of Delaware, Newark, DE (Uni↗
NASA NTRS1980

Lunar near-surface shear wave velocities at the Apollo landing sites as inferred from spectral amplitude ratios

The horizontal-to-vertical amplitude ratios of the long-period seismograms are reexamined to determine the shear wave velocity distributions at the Apollo 12, 14, 15, and 16 lunar landing sites. Average spectral ratios, computed from a number of impact signals, were compared with spectral ratios calculated for the fundamental mode Rayleigh waves in media consisting of homogeneous, isotropic, horizontal layers. The shear velocities of the best fitting models at the different sites resemble each other and differ from the average for all sites by not more than 20% except for the bottom layer at station 14. The shear velocities increase from 40 m/s at the surface to about 400 m/s at depths between 95 and 160 m at the various sites. Within this depth range the velocity-depth functions are well represented by two piecewise linear segments, although the presence of first-order discontinuities cannot be ruled out.

Horvath, P.↗
DOE OSTI2023

New Insights from Legacy Seismic Data regarding Basalt Elevations and Variability on the Hanford Site

Migration of groundwater contaminants in the Gable Gap area of the Hanford Site in southeastern Washington State is strongly influenced by the distribution and permeability of basalts that lie beneath an unconfined aquifer. Locally, folding and faulting of the Columbia River Basalt associated with the Yakima fold and thrust belt followed by erosion due to the Lake Missoula floods resulted in a complex basalt surface that represents either an impermeable lower boundary to the unconfined aquifer system or localized regions of increased permeability that potentially promote communication between the unconfined aquifer system and deeper, confined aquifer systems. Paleo-channels carved into the basalt by floodwaters are thought to provide preferential flow paths for groundwater contaminants. In 2011, a seismic landstreamer campaign was carried out to image the basalt surface and produced pre-stack depth migrated p-wave reflection images. The reflection images identified two large troughs that may represent paleo-channels and several areas of possible faulting. Here, the streamer data are re-analyzed using refraction travel-time and Rayleigh wave dispersion analyses to obtain images of compressional and shear wave velocities within the suprabasalt sediment sections and the upper basalt surface. The combined interpretation of reflection and seismic velocity images shows complexity in the basalt velocity and elevation, which varies by 50 m or more within the study area. These results, along with other ongoing geophysical investigations, will be used to inform the site geologic model and potentially guide placement of future boreholes needed to quantify vertical flow between the confined and unconfined aquifers.

58 GEOSCIENCES↗