Reflection and refraction seismic studies in the Great Salt Lake Desert, Utah

Geophysics ◽  
1988 ◽  
Vol 53 (4) ◽  
pp. 431-433 ◽  
Author(s):  
R. M. René ◽  
J. L. Fitter ◽  
D. J. Murray ◽  
J. K. Walters
Keyword(s):  
Salt Lake ◽  
Gravity Data ◽  
Great Salt Lake ◽  
P Wave ◽  
Unconsolidated Sediments ◽  
Gravity Modeling ◽  
Reflection Profile ◽  
Single Fold ◽  
Refraction Seismic ◽  
Basin Floor

Seismic refraction and CDP reflection profiles were acquired across mud flats of the Great Salt Lake Desert, Utah, during the summer of 1983. a combination of weight drops, horizontal hammers, buried explosives, and explosives detonated in air (Poulter method) was used. A 6.4 km refraction and single‐fold reflection profile indicates the presence of a shallow depression (Donner Reed basin) eastb of Donner Reed pass in the Silver Island Mountains. A basin floor ramp of Paleozoic rocks dipping approximately 30 degrees east into the Crater Island graben is interpreted beneath a 4.6 km 12-fold CDP reflection profile obtained by the Poulter method. This ramp extends beneath at least 0.8 km of condolidated Neogene sediments and 0.8 km of younger (largely unconsolidated) sediments. Weight‐drop and horizontal‐hammer profiles for the critical refraction along the Silurian Laketown dolomite yield P-wave and S-wave velocity estimates of 5270 ± 100 and [Formula: see text], respectively. The mud flats, with their laterally uniform finegrained sediments and shallow water table, provided excellent coupling of seismic energy. Air shots of 4.1 to 5.4 kg explosives without a source array gave good penetration to a depth of about 1.6 km. Partial migration before stack facilitated estimation of moveout velocities in the case of layers onlapping against a basin floor ramp, even though the maximum dips were only about 30 degrees. Gravity modeling and seismic ray tracing through intervals of constant velocity bounded by polynomial interfaces aided synergetic interpretation of the reflection, refraction, and gravity data.

Low‐cost geophysical investigations of a paleochannel aquifer in the Eastern Goldfields, Western Australia

Geophysics ◽  
2002 ◽  
Vol 67 (3) ◽  
pp. 690-700 ◽  
Author(s):  
Josef Holzschuh
Keyword(s):  
Water Table ◽  
Western Australia ◽  
Seismic Reflection ◽  
Wave Reflection ◽  
Gravity Data ◽  
P Wave ◽  
Gravity Modeling ◽  
S Wave ◽  
Sand And Gravel ◽  
Gravel Aquifer

Compressional (P) wave and shear (S) wave seismic reflection techniques were used to delineate the sand and gravel aquifer within a highly saline clay‐filled paleochannel in the Eastern Goldfields of Western Australia. The seismic refraction and gravity methods were also used to investigate the paleochannel. The unsaturated loose fine‐grained sand up to 10 m in depth at the surface is a major factor in degrading subsurface imaging. The seismic processing needed to be precise, with accurate static corrections and normal moveout corrections. Deconvolution enhanced the aquifer and other paleochannel reflectors. P‐wave reflection and refraction layer depths had good correlation and showed a total of six boundaries: (1) water table, (2) change in velocity (compaction) in the paleochannel sediments, (3) sand and gravel aquifer, (4) red‐brown saprolite and green saprolite boundary, (5) weathered bedrock, and (6) unweathered bedrock. P‐wave explosive and hammer sources were found to have similar signal characteristics, and the aquifer and bedrock were both imaged using the hammer source. The deep shots below the water table have the most broadband frequency response for reflections, but stacking clear reflections was difficult. The S‐wave reflection results showed high lateral and vertical resolution of the basal saprolite clay, the sand and gravel aquifer, and very shallow clays above the aquifer. The S‐wave reflection stacking velocities were 10–20% of the P‐waves, increasing the resolution of the S‐wave section. The gravity data were modelled to fit the known drilling and P‐wave seismic reflection depths. The refraction results did not identify the top of bedrock, so refraction depths were not used for the gravity modeling in this highly weathered environment. The final gravity model mapped the bedrock topography beyond the lateral extent of the seismic and drilling data.

Joint optimization of vertical component gravity and P-wave first arrivals by simulated annealing

Geophysics ◽  
2016 ◽  
Vol 81 (4) ◽  
pp. ID59-ID71 ◽  
Author(s):  
Kyle Basler-Reeder ◽  
John Louie ◽  
Satish Pullammanappallil ◽  
Graham Kent
Keyword(s):  
Simulated Annealing ◽  
Gravity Data ◽  
Vertical Component ◽  
Geothermal Field ◽  
P Wave ◽  
Joint Optimization ◽  
Gravity Modeling ◽  
Deep Basin ◽  
Data Set ◽  
Convolution Model

Joint seismic and gravity analyses of the San Emidio geothermal field in the northwest Basin and Range province of Nevada demonstrate that joint optimization changes interpretation outcomes. The prior 0.3–0.5 km deep basin interpretation gives way to a deeper than 1.3 km basin model. Kirchoff prestack depth migrations reveal that joint optimization ameliorates shallow velocity artifacts, flattening antiformal reflectors that could have been interpreted as folds. Furthermore, joint optimization provides a clearer picture of the rangefront fault by increasing the depth of constrained velocities, which improves reflector coherency at depth. This technique provides new insight when applied to existing data sets and could replace the existing strategy of forward modeling to match gravity data. We have achieved stable joint optimization through simulated annealing, a global optimization algorithm that does not require an accurate initial model. Balancing the combined seismic-gravity objective function is accomplished by a new approach based on analysis of Pareto charts. Gravity modeling uses an efficient convolution model, and the basis of seismic modeling is the highly efficient Vidale eikonal equation traveltime generation technique. Synthetic tests found that joint optimization improves velocity model accuracy and provides velocity control below the deepest headwave raypath. Restricted offset-range migration analysis provides insights into precritical and gradient reflections in the data set.

scholarly journals Crustal structure and evolution of the Niuafo'ou Microplate in the northeastern Lau Basin, Southwestern Pacific

2020 ◽  
Author(s):  
Florian Schmid ◽  
Heidrun Kopp ◽  
Michael Schnabel ◽  
Anke Dannowski ◽  
Ingo Heyde ◽  
...  
Keyword(s):  
Gravity Data ◽  
Seafloor Spreading ◽  
P Wave ◽  
Spreading Center ◽  
Plate Boundaries ◽  
Volcanic Arc ◽  
Lau Basin ◽  
Refraction Seismic ◽  
Wave Tomography ◽  
Back Arc

<p>The northeastern Lau Basin is one of the fastest opening and magmatically most active back-arc regions on Earth. Although the current pattern of plate boundaries and motions in this complex mosaic of microplates is fairly well understood, the structure and evolution of the back-arc crust are not. We present refraction seismic, multichannel seismic and gravity data from a 300 km long east-west oriented transect crossing the Niuafo’ou Microplate (back-arc), the Fonualei Rift and Spreading Centre (FRSC) and the Tofua Volcanic Arc at 17°20’S. Our P wave tomography model shows strong lateral variations in the thickness and velocity-depth distribution of the crust. The thinnest crust is present in the Fonualei Rift and Spreading Center, suggesting active seafloor spreading there. In the much thicker crust of the volcanic arc we identify a region of anomalously low velocities, indicative of partial melts. Surprisingly, the melt reservoir is located at ~17 km distance to the volcanic front, supporting the hypothesis that melts are deviated from the volcanic arc towards the FRSC in sub-crustal domains. We identify two distinct regions in the back-arc crust, representing different opening phases of the northeastern Lau Basin. During initial extension, likely dominated by rifting, crust of generally lower upper-crustal velocities formed. During an advanced opening phase, likely dominated by seafloor spreading, crust of higher upper-crustal velocities formed and is now up to 11 km thick. This thickening is the result of magmatic underplating, which is supported by elevated upper mantle temperatures in this region.</p>

Early Holocene Great Salt Lake, USA

2015 ◽  
Vol 84 (1) ◽  
pp. 57-68 ◽  
Author(s):  
Charles G. Oviatt ◽  
David B. Madsen ◽  
David M. Miller ◽  
Robert S. Thompson ◽  
John P. McGeehin
Keyword(s):  
Great Basin ◽  
Salt Lake ◽  
Great Salt Lake ◽  
Lake Basin ◽  
Basin Floor ◽  
Lake Floor ◽  
Sulfate Salts ◽  
Brine Shrimp Cysts ◽  
Surficial Deposits ◽  
Apparent Conflict

Shorelines and surficial deposits (including buried forest-floor mats and organic-rich wetland sediments) show that Great Salt Lake did not rise higher than modern lake levels during the earliest Holocene (11.5–10.2 cal ka BP; 10–9 14C ka BP). During that period, finely laminated, organic-rich muds (sapropel) containing brine-shrimp cysts and pellets and interbedded sodium-sulfate salts were deposited on the lake floor. Sapropel deposition was probably caused by stratification of the water column — a freshwater cap possibly was formed by groundwater, which had been stored in upland aquifers during the immediately preceding late-Pleistocene deep-lake cycle (Lake Bonneville), and was actively discharging on the basin floor. A climate characterized by low precipitation and runoff, combined with local areas of groundwater discharge in piedmont settings, could explain the apparent conflict between evidence for a shallow lake (a dry climate) and previously published interpretations for a moist climate in the Great Salt Lake basin of the eastern Great Basin.

Simulation of 3D elastic wave propagation in the Salt Lake Basin

1995 ◽  
Vol 85 (6) ◽  
pp. 1688-1710 ◽  
Author(s):  
Kim B. Olsen ◽  
James C. Pechmann ◽  
Gerard T. Schuster
Keyword(s):  
Salt Lake ◽  
Incidence Angle ◽  
P Wave ◽  
Surface Velocity ◽  
Unconsolidated Sediments ◽  
Lake Basin ◽  
P Waves ◽  
Near Surface ◽  
Rock Site ◽  
Particle Velocities

Abstract We have used a 3D finite-difference method to model 0.2 to 1.2 Hz elastodynamic site amplification in the Salt Lake Valley, Utah. The valley is underlain by a sedimentary basin, which in our model has dimensions of 48 by 25 by 1.3 km. Simulations are carried out for a P wave propagating vertically from below and for P waves propagating horizontally to the north, south, east, and west in a two-layer model consisting of semi-consolidated sediments surrounded by bedrock. Results show that in general, sites with the largest particle velocities, cumulative kinetic energies, duration times of motion, and spectral magnitudes overlie the deepest parts of the basin. The maximum values of these parameters are generally found above steeply dipping parts of the basin walls. The largest vector particle velocities are associated with P or SV waves that come from within 10° of the source azimuth. Low-energy S and surface waves follow the strongest arrivals. The largest peak particle velocities, cumulative kinetic energies, signal durations, and spectral magnitudes in the simulations are, respectively, 2.9, 15.9, 40.0, and 3.5 times greater than the values at a rock site measured on the component parallel to the propagation direction of the incident P wave. Scattering and/or mode conversions at the basin boundaries contribute significantly to the signal duration times. As a check on the validity of our simulations, we compared our 3D synthetic seismograms for the vertically incident plane P wave to seismograms of nearly vertically incident teleseismic P waves recorded at an alluvium site in the valley and at a nearby rock site. The 3D synthetics for the alluvium site overestimate the relatively small amplification of the initial P wave and underestimate the large amplification of the coda. Using 2D simulations, we find that most of the discrepancies between the 3D synthetic and observed records can be explained by an apparently incorrect total sediment thickness, omission from the model of the near-surface low-velocity unconsolidated sediments and of attenuation, and the inexact modeling of the incidence angle of the teleseism. The records from a 2D simulation in which these deficiencies are remedied (with Q = 65), and which also includes topography and a near-surface velocity gradient in the bedrock, provide a better match to the teleseismic data than the records from the simple two-layer 3D simulation. Our results suggest that for steeply incident P waves, the impedance decrease and resonance effects associated with the deeper basin structure control the amplification of the initial P-wave arrival, whereas reverberations in the near-surface unconsolidated sediments generate the large-amplitude coda. These reverberations are caused mainly by P-to-S converted waves, and their strength is therefore highly sensitive to the incidence angle of the source.

scholarly journals A Constrained 3D Density Model of the Upper Crust from Gravity Data Interpretation for Central Costa Rica

2010 ◽  
Vol 2010 ◽  
pp. 1-9 ◽  
Author(s):  
Oscar H. Lücke ◽  
Hans-Jürgen Götze ◽  
Guillermo E. Alvarado
Keyword(s):  
Costa Rica ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
Data Interpretation ◽  
P Wave ◽  
Density Model ◽  
Arc Magmatism ◽  
Upper Crust ◽  
Velocity Models ◽  
Refraction Seismic

The map of complete Bouguer anomaly of Costa Rica shows an elongated NW-SE trending gravity low in the central region. This gravity low coincides with the geographical region known as the Cordillera Volcánica Central. It is built by geologic and morpho-tectonic units which consist of Quaternary volcanic edifices. For quantitative interpretation of the sources of the anomaly and the characterization of fluid pathways and reservoirs of arc magmatism, a constrained 3D density model of the upper crust was designed by means of forward modeling. The density model is constrained by simplified surface geology, previously published seismic tomography and P-wave velocity models, which stem from wide-angle refraction seismic, as well as results from methods of direct interpretation of the gravity field obtained for this work. The model takes into account the effects and influence of subduction-related Neogene through Quaternary arc magmatism on the upper crust.

Bibliographic notes on H. Stansbury's Exploration and survey of …/ Expedition to the valley of the Great Salt Lake

2003 ◽  
Vol 30 (2) ◽  
pp. 317-330 ◽  
Author(s):  
L. J. Dorr ◽  
D. H. Nicolson ◽  
L. K. Overstreet
Keyword(s):  
Salt Lake ◽  
Great Salt Lake ◽  
Title Page ◽  
Classic Work ◽  
Us Government ◽  
Multiple Issues ◽  
Title Pages

Howard Stansbury's classic work is bibliographically complex, with two true editions as well as multiple issues of the first edition. The first edition was printed in Philadelphia; its 487 stereotyped pages were issued in 1852 under two different titles with three variant title-pages (an official US government issue and two trade issues). A second edition was printed in Washington in 1853 and had 495 typeset pages (with corrections and additions in the appendices). The issue of 1855 is identical to the 1852 trade issue, except for the change of the date on the title-page. Each issue and edition, with its bindings and plates, is described.

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