Geology Reports⌕ Search

SEARCH · Geology Reports

Results for “Journal of Geological Research”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 883 records · Page 49Linked to original sources
USGS2024

Insights into glendonite formation from the upper Oligocene Sagavanirktok Formation, North Slope, Alaska

The type locality for the upper Oligocene Nuwok Member of the Sagavanirktok Formation (Carter Creek, North Slope, Alaska, USA) contains abundant occurrence of glendonite, a pseudomorph after the calcium carbonate mineral ikaite, which typically forms in the shallow subsurface of cold marine sediments. The region during the time of Nuwok Member deposition was located at a high latitude, similar to today, and the study site is characterized by sands and silty muds interpreted here to have been deposited in coastal and shelfal marine environments. Isotopic (Sr) and biostratigraphic (foraminifera) evidence presented here refine the depositional age of the outcrop to approximately 24 Ma. Glendonites occur in two basic forms: radial clusters, commonly centered around a single larger primary crystal ( approx. 10 cm; Type A) and larger single blades generally without accessory crystals (approx. 15–25 cm; Type B). Microscopic examination revealed a sequence of multiple types of replacive calcite that formed as a direct result of ikaite transformation: Type 1 rhombohedral crystals characterized by microporous and inclusion-rich cores and concentric zones, Type 2A, composed of clear calcite that overgrew and augmented Type 1 crystals, and inclusion-rich, microcrystalline Type 2B, which formed a matrix surrounding the rhombs and commonly dominates the outer rims of glendonite specimens. Type 3 calcite precipitated as fibrous, botryoidal epitaxial cement atop previous phases and is not ikaite-derived. These phases are distributed in similar ways in all examined specimens and are consistent with several previously described glendonite occurrences around the world, despite differing diagenetic and geologic histories. Stable isotope evidence (δ13C and δ18O) suggests sourcing of glendonite carbon from both organic and methanogenic sources. Glendonites of the Nuwok Member can therefore assist in the determination of a more comprehensive ikaite transformation model, improving our understanding of glendonite formation and the sedimentological and environmental context of their occurrence. Oligocene glendonites are uncommon globally; the well-preserved occurrence described here can allow future studies to better reconstruct Arctic environmental conditions and paleoclimates during this time.

Alaska↗
USGS2009

Coastline shifts and probable ship landing site submerged off ancient Locri-Epizefiri, southern Italy

A geophysical survey provides new information on marine features located seaward of Locri-Epizefiri (Locri), an ancient Greek settlement on the Ionian coastal margin in southern Italy. The study supplements previous work by archaeologists who long searched for the site's harbor and recently identified what was once a marine basin that is now on land next to the city walls of Locri. Profiles obtained offshore, between the present coast and outer shelf, made with a high-resolution, seismic subbottom-profiling system, record spatial and temporal variations of buried Holocene deposits. Two of these submerged features are part of a probable now-submerged ship landing facility. The offshore features can be linked to coastline displacements that occurred off Locri: a sea-to-land shift before Greek settlement, followed by a shoreline reversal from the archaeological site back to sea, and more recently, a return landward. The seaward directed coastal shift that occurred after Locri's occupation by Greeks was likely caused by land uplift near the coastal margin and tectonic seaward shift of the coast, as documented along this geologically active sector of the Calabrian Arc. The seismic survey records an angular, hook-shaped, low rise that extends from the present shore and is now buried on the inner shelf. The rise, enclosing a core lens of poorly stratified to transparent acoustic layers, bounds a broad, low-elevation zone positioned immediately seaward of the shoreline. Close proximity of the raised feature to the low-elevation area suggests it may have been a fabricated structure that functioned as a wave-break for a ship-landing site. The study indicates that the basin extended offshore as a function of the coastline's seaward migration during and/or after Greek occupation of Locri.

Journal of Coastal Research↗
USGS2015

Enhanced microbial coalbed methane generation: A review of research, commercial activity, and remaining challenges

Coalbed methane (CBM) makes up a significant portion of the world’s natural gas resources. The discovery that approximately 20% of natural gas is microbial in origin has led to interest in microbially enhanced CBM (MECoM), which involves stimulating microorganisms to produce additional CBM from existing production wells. This paper reviews current laboratory and field research on understanding processes and reservoir conditions which are essential for microbial CBM generation, the progress of efforts to stimulate microbial methane generation in coal beds, and key remaining knowledge gaps. Research has been primarily focused on identifying microbial communities present in areas of CBM generation and attempting to determine their function, in-situ reservoir conditions that are most favorable for microbial CBM generation, and geochemical indicators of metabolic pathways of methanogenesis (i.e., acetoclastic or hydrogenotrophic methanogenesis). Meanwhile, researchers at universities, government agencies, and companies have focused on four primary MECoM strategies: 1) microbial stimulation (i.e., addition of nutrients to stimulate native microbes); 2) microbial augmentation (i.e., addition of microbes not native to or abundant in the reservoir of interest); 3) physically increasing microbial access to coal and distribution of amendments; and 4) chemically increasing the bioavailability of coal organics. Most companies interested in MECoM have pursued microbial stimulation: Luca Technologies, Inc., successfully completed a pilot scale field test of their stimulation strategy, while two others, Ciris Energy and Next Fuel, Inc., have undertaken smaller scale field tests. Several key knowledge gaps remain that need to be addressed before MECoM strategies can be implemented commercially. Little is known about the bacterial community responsible for coal biodegradation and how these microorganisms may be stimulated to enhance microbial methanogenesis. In addition, research is needed to understand what fraction of coal is available for biodegradation, and methods need to be developed to determine the extent of in-situ coal biodegradation by MECoM processes for monitoring changes to coal quality. Questions also remain about how well field-scale pilot tests will scale to commercial production, how often amendments will need to be added to maintain new methane generation, and how well MECoM strategies transfer between coal basins with different formation water geochemistries and coal ranks. Addressing these knowledge gaps will be key in determining the feasibility and commercial viability of MECoM technology.

International Journal of Coal Geology↗
USGS1999

Does Europa have a subsurface ocean? Evaluation of the geological evidence

It has been proposed that Jupiter's satellite Europa currently possesses a global subsurface ocean of liquid water. Galileo gravity data verify that the satellite is differentiated into an outer H 2 O layer about 100 km thick but cannot determine the current physical state of this layer (liquid or solid). Here we summarize the geological evidence regarding an extant subsurface ocean, concentrating on Galileo imaging data. We describe and assess nine pertinent lines of geological evidence: impact morphologies, lenticulae, cryovolcanic features, pull‐apart bands, chaos, ridges, surface frosts, topography, and global tectonics. An internal ocean would be a simple and comprehensive explanation for a broad range of observations; however, we cannot rule out the possibility that all of the surface morphologies could be due to processes in warm, soft ice with only localized or partial melting. Two different models of impact flux imply very different surface ages for Europa; the model favored here indicates an average age of ∼50 Myr. Searches for evidence of current geological activity on Europa, such as plumes or surface changes, have yielded negative results to date. The current existence of a global subsurface ocean, while attractive in explaining the observations, remains inconclusive. Future geophysical measurements are essential to determine conclusively whether or not there is a liquid water ocean within Europa today.

Journal of Geophysical Research: Planets↗
USGS2012

The McKinley Sequence of granitic rocks: A key element in the accretionary history of southern Alaska

The McKinley sequence of granitic rocks consists of several discrete plutons in the central Alaska Range. Most of these plutons crop out south of the Denali fault system (DFS) in the Talkeetna quadrangle. Plutons of the McKinley sequence largely intrude deformed upper Meszoic flysch between the DFS and the northern edges of Wrangellia and the Peninsular terrane, which jointly make up the Talkeetna superterrane. The average K-Ar age of biotite from nine granites of the McKinley sequence is 57.3 Ma; Rb-Sr data for whole rock samples indicate that the McKinley sequence cannot be older than 60 Ma. A selected suite of 20 samples of granite and granodiorite range in SiO 2 from 65.9 to 77.6%. All 20 samples are corundum normative, and 18 are moderately peraluminous. Initial 87 Sr/ 86 Sr ratios range from 0.7054 to 0.7085. The σ 18 O values range from +11.2 to +14.6‰. These high and variable Sr isotopic ratios, peraluminous nature, rare earth element patterns, and high σ 18 O values suggest that granitic rocks of the McKinley sequence crystallized from hybrid magmas produced by assimilation of sedimentary rocks by a mantle-derived melt. Mesozoic flysch is the likely source of the crustal component of the hybrid magmas. Geologic evidence suggests that the Talkeetna superterrane collided with stable Alaska after Early Cretaceous time. The flysch basin, lying south of stable Alaska, was closed by northward movement of the Talkeetna superterrane; maximum age for basin closure and terrane accretion is middle Cretaceous (Cenomanian). Paleomagnetic evidence indicates that all terranes north of the DFS have been part of stable Alaska since the Paleocene and that northward movement of Wrangellia was completed by 50 Ma. Granitic rocks of the McKinley sequence may be products of terrane accretion; the granitic rocks crystallized from hybrid magmas produced during terrane collision and deformation of the flysch basin. Isotopic ages of the McKinley sequence establish the time of final accretion of the Talkeetna superterrane as Paleocene.

Journal of Geophysical Research Solid Earth↗
USGS2012

Overview of the structure and geothermal potential of Newberry Volcano, Oregon

Evidence from a broad range of geological and geophysical investigations of Newberry Volcano in central Oregon suggests the presence of a small magma body beneath the summit caldera. Drilling has encountered temperatures indicative of a hydrothermal system above the hypothesized magma body. On the basis of hydrothermal mineralogy the temperature of the hydrothermal system is at or near its maximum value, indicating that the hydrothermal system is young. Basaltic underplating is postulated to replenish the magma body. The results of interdisciplinary studies at Newberry Volcano document that young, silicic volcanism in the Cascade Range can have geothermal potential. These results should be applied with caution to the rest of the Cascade Range because of the strong influence of Basin and Range extensional tectonics on Newberry Volcano's style of volcanism.

Journal of Geophysical Research Solid Earth↗
USGS1995

The Uwekahuna Ash Member of the Puna Basalt: product of violent phreatomagmatic eruptions at Kilauea volcano, Hawaii, between 2800 and 2100 14C years ago

Kilauea volcano's reputation for relatively gentle effusive eruptions belies a violent geologic past, including several large phreatic and phreatomagmatic eruptions that are recorded by Holocene pyroclastic deposits which mantle Kilauea's summit area and the southeast flank of adjacent Mauna Loa volcano. The most widespread of these deposits is the Uwekahuna Ash Member, a basaltic surge and fall deposit emplaced during two or more eruptive episodes separated by a few decades to several centuries. It is infered that the eruptions which produced the Uwekahuna were driven by water interacting with a fluctuating magma column. The volume, extent and character of the Uwekahuna deposits underscore the hazards posed by relatively infrequent but potentially devastating explosive eruptions at Kilauea, as well as at other basaltic volcanoes. -from Authors

Journal of Volcanology and Geothermal Research↗
USGS2014

The National Climate Change and Wildlife Science Center annual report for 2013

In 2008, Congress created the National Climate Change and Wildlife Science Center (NCCWSC) within the U.S. Geological Survey (USGS). The center was formed to respond to the demands of natural resource managers for rigorous scientific information and effective tools for assessing and responding to climate change. Located at the USGS National Headquarters in Reston, Va., the NCCWSC has invested more than $93 million (through FY13) in cutting-edge climate change research and, in response to Secretarial Order No. 3289, established and is managing eight regional Department of Interior (DOI) Climate Science Centers (CSCs). In 2013: The DOI CSCs awarded nearly $7 million in funding to universities and other partners for climate and land-use change research. The scientific work of the NCCWSC-CSC enterprise moved toward projects that focus on ‘Science Infrastructure and Capacity Building’ and ‘Thematic Science’. A permanent director, David Helweg, Ph.D., was hired for the Pacific Islands CSC (PI CSC), completing the CSC leadership team. Staff scientists were hired at the Alaska (AK), Northeast (NE), and Southeast (SE) CSCs. Each of the eight CSCs completed the formation of regional Stakeholder Advisory Committees (SACs) and a national advisory committee (ACCCNRS) was created to oversee the NCCWSC-CSC enterprise. NCCWSC staff worked on creating a searchable public database on climate change vulnerability assessments. NCCWSC scientists authored articles in a special issue of the Ecological Society of America’s journal Frontiers in Ecology and the Environment, which was devoted to an assessment of climate change effects on biodiversity and ecosystems, and the consequences for people. Learn more about these achievements in The National Climate Change and Wildlife Science Center Annual Report for 2013 .

Circular↗
USGS2019

A process-based model of pre-eruption seismicity patterns and its use for eruption forecasting at dormant stratovolcanoes

Using long-term data sets, the eruptive size, timing and style can typically be successfully forecast for dormant volcanoes using current monitoring data and knowledge of precursory eruptive patterns. The USAID-USGS Volcano Disaster Assistance Program (VDAP) utilizes seismic data over multiple eruption cycles and across volcano types to successfully forecast eruption size, style and onset times, as well as changes within ongoing eruptions. From millions of seismic event observations, we show that seismic data, a proxy for rate-dependent strain changes in the magmatic system, combined with a process-based conceptual geologic model enables eruption forecasting, especially for stratovolcanoes dormant >20 years. We show that this model often works for some open systems, ones that sufficiently reseal to plug the conduit, and also where a deep intrusion occurs after phreatic or phreatomagmatic explosions have begun. This model is divided into four seismicity and geologic stages. We describe each of the four stages of seismicity in detail and how they relate to the ongoing geologic process of that stage: Stage 1. Deep intrusion and seismicity occurring at 10 to 40 + km depth below the volcanic edifice; Stage 2. Distal VT seismicity induced at distances from 2 to >30 km laterally from the summit by magma intruding into and inflating the upper-crustal magma storage region; Stage 3. Vent-clearing seismicity associated with the initial vent creation and clearing phase of eruptive activity. Stage 4. Repetitive event seismicity associated with the final ascent of magma from 2 km to the surface. We present 36 examples of this seismic progression from 26 volcanoes. We believe that this progression generally correlates with the magma flux and the eventual explosivity and is invaluable for forecasting eruptions.

Journal of Volcanology and Geothermal Research↗
USGS1999

Stratigraphic constraints on the timing and emplacement of the Alika 2 giant Hawaiian submarine landslide

Previous work has found evidence for giant tsunami waves that impacted the coasts of Lanai, Molokai and other southern Hawaiian Islands, tentatively dated at 100 + and 200 + ka by U-series methods on uplifted coral clasts. Seafloor imaging and related work off Hawaii Island has suggested the Alika phase 2 debris avalanche as the source of the ~ 100 ka "giant wave deposits", although its precise age has been elusive. More recently, a basaltic sand bed in ODP site 842 (~ 300 km west of Hawaii) estimated at 100 ?? 20 ka has been suggested to correlate with this or another large Hawaiian landslide. Our approach to the timing and linkage of giant submarine landslides and paleo-tsunami deposits is a detailed stratigraphic survey of pelagic deposits proximal to the landslide feature, beginning with a suite of seven piston, gravity and box cores collected in the vicinity of the Alika 2 slide. We used U-series dating techniques, including excess 230 Th and 210 Pb profiling, high-resolution paleomagnetic stratigraphy, including continuous, U-channel analysis, δ 18 O stratigraphy, visual and X-ray sediment lithology, and the petrology and geochemistry of the included turbidites and ash layers. Minimum ages for the Alika phase 2a slide from detailed investigation of two of the cores are 112 ± 15 ka and 125 ± 24 ka (2σ) based on excess 230 Th dating. A less precise age for the Alika phase 1 and/or South Kona slide is 242 ± 80 ka (2σ), consistent with previous geological estimates. Oxygen isotope analyses of entrained planktonic foraminifera better constrain the Alika phase 2a maximum age at 127 ± 5 ka, which corresponds to the beginning of the stage 5e interglacial period. It is proposed that triggering of these giant landslides may be related to climate change when wetter periods increase the possibility of groundwater intrusion and consequent phreatomagmatic eruptions of shallow magma chambers. Our study indicates the contemporaneity of the Alika giant submarine landslides and distal deposits from enormous turbidity currents as well as coral clasts reported to be tsunami deposits on Lanai and Molokai through direct dating and compositional analysis of the landslide deposits.

Journal of Volcanology and Geothermal Research↗
USGS2003

Selection of the Mars Exploration Rover landing sites

The selection of Meridiani Planum and Gusev crater as the Mars Exploration Rover landing sites took over 2 years, involved broad participation of the science community via four open workshops, and narrowed an initial ∼155 potential sites (80–300 × 30 km) to four finalists based on science and safety. Engineering constraints important to the selection included (1) latitude (10°N–15°S) for maximum solar power, (2) elevation (less than −1.3 km) for sufficient atmosphere to slow the lander, (3) low horizontal winds, shear, and turbulence in the last few kilometers to minimize horizontal velocity, (4) low 10‐m‐scale slopes to reduce airbag spin‐up and bounce, (5) moderate rock abundance to reduce abrasion or strokeout of the airbags, and (6) a radar‐reflective, load‐bearing, and trafficable surface safe for landing and roving that is not dominated by fine‐grained dust. The evaluation of sites utilized existing as well as targeted orbital information acquired from the Mars Global Surveyor and Mars Odyssey. Three of the final four landing sites show strong evidence for surface processes involving water and appear capable of addressing the science objectives of the missions, which are to determine the aqueous, climatic, and geologic history of sites on Mars where conditions may have been favorable to the preservation of evidence of possible prebiotic or biotic processes. The evaluation of science criteria placed Meridiani and Gusev as the highest‐priority sites. The evaluation of the three most critical safety criteria (10‐m‐scale slopes, rocks, and winds) and landing simulation results indicated that Meridiani and Elysium Planitia are the safest sites, followed by Gusev and Isidis Planitia.

Journal of Geophysical Research E: Planets↗
USGS2012

The emplacement of ophiolites by collision

Ophiolites, recognized in most of the world's orogenic belts, are generally interpreted to be oceanic crust and upper mantle (lithosphere) fragments that have been incorporated into continental margins at consuming plate boundaries. We suggest that the mechanism for ophiolite emplacement is the same in both the Alpine and Andean-type orogenes. In both geological settings, obduction of oceanic lithosphere onto the continental lithosphere is caused by the convergence of light, buoyant bodies such as oceanic plateaus, continental slivers, island arcs, or old hot spot traces. For example, the Troodos ophiolite complex, previously interpreted by some workers as resulting from continental collision, may have been emplaced by the collision of Cyprus with the Eratosthenes Plateau embedded in the oceanic eastern Mediterranean crust. On the other hand, the Upper Jurassic Coast Range Ophiolites of California, previously interpreted as resulting from typical oceanic subduction, may be the result of a continuous injection of thick nonsubductable packages of light, continentally derived sedimentary rocks, seamounts, and plateaus into the subduction zones. Many other ophiolite complexes may be similarly related to accreted terranes.

Journal of Geophysical Research↗
USGS1996

Seismic tomography and deformation modeling of the junction of the San Andreas and Calaveras faults

Local earthquake P traveltime data is inverted to obtain a three-dimensional tomographic image of the region centered on the junction of the San Andreas and Calaveras faults. The resulting velocity model is then used to relocate more than 17,000 earthquakes and to produce a model of fault structure in the region. These faults serve as the basis for modeling the topography using elastic dislocation methods. The region is of interest because active faults join, it marks the transition zone from creeping to locked fault behavior on the San Andreas fault, it exhibits young topography, and it has a good spatial distribution of seismicity. The tomographic data set is extensive, consisting of 1445 events, 96 stations, and nearly 95,000 travel time readings. Tomographic images are resolvable to depths of 12 km and show significant velocity contrasts across the San Andreas and Calaveras faults, a low-velocity zone associated with the creeping section of the San Andreas fault, and shallow low-velocity sediments in the southern Santa Clara valley and northern Salinas valley. Relocated earthquakes only occur where v p > 5 km/s and indicate that portions of the San Andreas and Calaveras faults are non vertical, although we cannot completely exclude the possibility that all or part of this results from ray tracing problems. The new dips are more consistent with geological observations that dipping faults intersect the surface where surface traces have been mapped. The topographic modeling predicts extensive subsidence in regions characterized by shallow low-velocity material, presumably the result of recent sedimentation. Some details of the topography at the junction of the San Andreas and Calaveras faults are not consistent with the modeling results, suggesting that the current position of this “triple junction” has changed with time. The model also predicts those parts of the fault subject to contraction or extension perpendicular to the fault strike and hence the sense of any dip-slip component. In each locality the relative vertical motion across the fault is consistent with the fault dips found with the new hypocentral locations.

Journal of Geophysical Research B: Solid Earth↗
USGS1998

Comparative geology and geochemistry of sedimentary-rock-hosted (Carlin Type) gold deposits in the People's Republic of China and in Nevada, USA

Sedimentary-rock-hosted (Carlin-type) gold deposits have been considered economically significant and geologically distinct since the early 1960's. This report consists of a nine-part text and an interactive database. This small database is to help Western companies get more information about these gold deposits in China, and to help geologists who are interested in world Carlin-type deposits conduct research on them. Because of their economic significance and geological distinctiveness, these deposits have caught the interest of economic geologists all over the world since the early 1960's. Similar deposits have been discovered in China, Australia, Dominican Republic, Spain, and Russia besides Nevada. Perhaps most significant are the 165 Carlin-type gold deposits that were found in southwest China during the past 15 years. Of these, at least 19 deposits have proven to be of substantial tonnage, making China the second leading country to exploit such deposits. With the increasing interest in Chinese Carlin-type gold deposits, some western companies and geologists desire to get more information about these Chinese deposits. This seems to have been very difficult because the literature was in Chinese. It is estimated that several hundred scientific publications (including papers, books, and technical reports) have been published. This database of Chinese Carlin-type Gold deposits is built on the documentation published during the most recent 10 years and includes six subjects, which consist of 165 records and 30 fields. A new Proterozoic-age sedimentary-rock-hosted gold deposit in northeastern P.R. China also is described. Note that for the old version 1.1 on the CD-ROM, the latitude and longitude locations of the mineral occurrences have been estimated from sketch maps and journal articles and are not intended for digital analysis. One of the improvements in this version 1.2 is the accuracy of geographic data. Version 1.3 updates to the database and includes maps and photos of deposits, deposit information and a geochemical model. See the version history for details.

Open-File Report↗
USGS2026

On the importance of ichthyoplankton monitoring for invasive grass carp control in the Laurentian Great Lakes

Grass carp ( Ctenopharyngodon idella ) is an invasive herbivore observed in small numbers in the Laurentian Great Lakes since the 1980 s with records from all lakes except Lake Superior. Identification of diploid, age-1 + grass carp from the Sandusky River, a Lake Erie tributary, in 2012, prompted targeted efforts to evaluate the status of grass carp reproduction in the Lake Erie Basin. In 2014, researchers from the U.S. Geological Survey and University of Toledo began surveys to assess grass carp spawning in the Great Lakes, with the first fertilized eggs discovered in 2015 in the Sandusky River. Eight Great Lakes tributaries in the United States have been surveyed for evidence of grass carp spawning, identifying three confirmed spawning tributaries (Sandusky, Maumee, and Huron Rivers in Ohio). Initial work identified specific flow and temperature conditions that likely stimulate spawning. Egg and larval drift modeling estimated spawning locations based on egg development and flow characteristics, which helped removal crews locate and target spawning fish in the Sandusky River and later, the Maumee River. The research synthesized herein demonstrates the value of ichthyoplankton research to inform control of emerging invasive species and could inform management of other invasive carps with similar reproductive life histories, should they enter the Great Lakes.

Michigan, Ohio↗
USGS2001

Interior trough deposits on Mars: Subice volcanoes?

Widespread, several-kilometer-thick successions of layered deposits occur as mounds that partly fill the troughs or chasmata that compose the Valles Marineris on Mars. Like terrestrial subice volcanoes, the layered deposits occur in a volcano-tectonic setting within basins that may have held ponded water or ice. On the basis of their dimensions, morphologies, and associated catastrophic floods and other geologic events as shown in Viking and new Mars Global Surveyor (MGS) data sets, we suggest that the interior deposits are volcanic in origin and possibly generated by subice eruptions. A tuya origin for the mounds can explain the lack of external sediment, mound heights that can rival the plateau, local flat-topped mesas, morphologically distinct mounds of different ages, horizontal to steep dips, fine-grained materials, indications of rare volcanic vents and lava flows, and spectral composition. The extremely diverse layering of west Candor Chasma and possible volcanic cones in Melas may have formed by related subaerial eruptions. Consistent with the suggestion that interior deposits are eroding out of the wall rock, some deposits could have been erupted from sites along the walls.

Journal of Geophysical Research E: Planets↗
USGS2006

Frictional strength heterogeneity and surface heat flow: Implications for the strength of the creeping San Andreas fault

Heat flow measurements along much of the San Andreas fault (SAF) constrain the apparent coefficient of friction (??app) of the fault to <0.2, much lower than laboratory-derived friction values for most geologic materials. However, heat flow data are sparse near the creeping section of the SAF, a frictional "asperity" where the fault slips almost exclusively by aseismic creep. We test the hypothesis that the creeping section has a substantially higher or lower ?? app than adjacent sections of the SAF. We use numerical models to explore the effects of faults with spatially and temporally heterogeneous frictional strength on the spatial distribution of surface heat flow. Heat flow from finite length asperities is uniformly lower than predicted by assuming an infinitely long fault. Over geologic time, lateral offset from strike-slip faulting produces heat flow patterns that are asymmetric across the fault and along strike. We explore a range of asperity sizes, slip rates, and displacement histories for comparing predicted spatial patterns of heat flow with existing measurements. Models with ??app ??? 0.1 fit the data best. For most scenarios, heat flow anomalies from a frictional asperity with ??app > 0.2 should be detectable even with the sparse existing observations, implying that ??app for the creeping section is as low as the surrounding SAF. Because the creeping section does not slip in large earthquakes, the mechanism controlling its weakness is not related to dynamic processes resulting from high slip rate earthquake ruptures. Copyright 2006 by the American Geophysical Union.

Journal of Geophysical Research B: Solid Earth↗
USGS2010

Silica in a Mars analog environment: Ka u Desert, Kilauea Volcano, Hawaii

Airborne Visible/Near-Infrared Imaging Spectrometer (AVIRIS) data acquired over the Ka u Desert are atmospherically corrected to ground reflectance and used to identify the mineralogic components of relatively young basaltic materials, including 250-700 and 200-400 year old lava flows, 1971 and 1974 flows, ash deposits, and solfatara incrustations. To provide context, a geologic surface units map is constructed, verified with field observations, and supported by laboratory analyses. AVIRIS spectral endmembers are identified in the visible (0.4 to 1.2 ??m) and short wave infrared (2.0 to 2.5 ??m) wavelength ranges. Nearly all the spectral variability is controlled by the presence of ferrous and ferric iron in such minerals as pyroxene, olivine, hematite, goethite, and poorly crystalline iron oxides or glass. A broad, nearly ubiquitous absorption feature centered at 2.25 ??m is attributed to opaline (amorphous, hydrated) silica and is found to correlate spatially with mapped geologic surface units. Laboratory analyses show the silica to be consistently present as a deposited phase, including incrustations downwind from solfatara vents, cementing agent for ash duricrusts, and thin coatings on the youngest lava flow surfaces. A second, Ti-rich upper coating on young flows also influences spectral behavior. This study demonstrates that secondary silica is mobile in the Ka u Desert on a variety of time scales and spatial domains. The investigation from remote, field, and laboratory perspectives also mimics exploration of Mars using orbital and landed missions, with important implications for spectral characterization of coated basalts and formation of opaline silica in arid, acidic alteration environments. Copyright 2010 by the American Geophysical Union.

Journal of Geophysical Research E: Planets↗