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

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At least 73 records · Page 4Linked to original sources
USGS2009

Slip maxima at fault junctions and rupturing of barriers during the 2008 Wenchuan earthquake

The disastrous 12 May 2008 Wenchuan earthquake in China took the local population as well as scientists by surprise. Although the Longmen Shan fault zonewhich includes the fault segments along which this earthquake nucleatedwas well known, geologic and geodetic data indicate relatively low (<3 mm yr -1 ) deformation rates. Here we invert Global Positioning System and Interferometric Synthetic Aperture Radar data to infer fault geometry and slip distribution associated with the earthquake. Our analysis shows that the geometry of the fault changes along its length: in the southwest, the fault plane dips moderately to the northwest but becomes nearly vertical in the northeast. Associated with this is a change in the motion along the fault from predominantly thrusting to strike-slip. Peak slip along the fault occurs at the intersections of fault segments located near the towns of Yingxiu, Beichuan and Nanba, where fatalities and damage were concentrated. We suggest that these locations represent barriers that failed in a single event, enabling the rupture to cascade through several fault segments and cause a major moment magnitude (M w ) 7.9 earthquake. Using coseismic slip distribution and geodetic and geological slip rates, we estimate that the failure of barriers and rupture along multiple segments takes place approximately once in 4,000 years. ?? 2009 Macmillan Publishers Limited. All rights reserved.

Nature Geoscience↗
USGS2009

Earth system sensitivity inferred from Pliocene modelling and data

Quantifying the equilibrium response of global temperatures to an increase in atmospheric carbon dioxide concentrations is one of the cornerstones of climate research. Components of the Earths climate system that vary over long timescales, such as ice sheets and vegetation, could have an important effect on this temperature sensitivity, but have often been neglected. Here we use a coupled atmosphere-ocean general circulation model to simulate the climate of the mid-Pliocene warm period (about three million years ago), and analyse the forcings and feedbacks that contributed to the relatively warm temperatures. Furthermore, we compare our simulation with proxy records of mid-Pliocene sea surface temperature. Taking these lines of evidence together, we estimate that the response of the Earth system to elevated atmospheric carbon dioxide concentrations is 30-50% greater than the response based on those fast-adjusting components of the climate system that are used traditionally to estimate climate sensitivity. We conclude that targets for the long-term stabilization of atmospheric greenhouse-gas concentrations aimed at preventing a dangerous human interference with the climate system should take into account this higher sensitivity of the Earth system. ?? 2010 Macmillan Publishers Limited. All rights reserved.

Nature Geoscience↗
USGS2010

Vulnerability of deep groundwater in the Bengal Aquifer System to contamination by arsenic

Shallow groundwater, the primary water source in the Bengal Basin, contains up to 100 times the World Health Organization (WHO) drinking-water guideline of 10g l 1 arsenic (As), threatening the health of 70 million people. Groundwater from a depth greater than 150m, which almost uniformly meets the WHO guideline, has become the preferred alternative source. The vulnerability of deep wells to contamination by As is governed by the geometry of induced groundwater flow paths and the geochemical conditions encountered between the shallow and deep regions of the aquifer. Stratification of flow separates deep groundwater from shallow sources of As in some areas. Oxidized sediments also protect deep groundwater through the ability of ferric oxyhydroxides to adsorb As. Basin-scale groundwater flow modelling suggests that, over large regions, deep hand-pumped wells for domestic supply may be secure against As invasion for hundreds of years. By contrast, widespread deep irrigation pumping might effectively eliminate deep groundwater as an As-free resource within decades. Finer-scale models, incorporating spatial heterogeneity, are needed to investigate the security of deep municipal abstraction at specific urban locations. ?? 2010 Macmillan Publishers Limited. All rights reserved.

Nature Geoscience↗
USGS2010

Groundwater sustainability strategies

Groundwater extraction has facilitated significant social development and economic growth, enhanced food security and alleviated drought in many farming regions. But groundwater development has also depressed water tables, degraded ecosystems and led to the deterioration of groundwater quality, as well as to conflict among water users. The effects are not evenly spread. In some areas of India, for example, groundwater depletion has preferentially affected the poor. Importantly, groundwater in some aquifers is renewed slowly, over decades to millennia, and coupled climate–aquifer models predict that the flux and/or timing of recharge to many aquifers will change under future climate scenarios. Here we argue that communities need to set multigenerational goals if groundwater is to be managed sustainably.

Nature Geoscience↗
USGS2010

An integrated perspective of the continuum between earthquakes and slow-slip phenomena

The discovery of slow-slip phenomena has revolutionized our understanding of how faults accommodate relative plate motions. Faults were previously thought to relieve stress either through continuous aseismic sliding, or as earthquakes resulting from instantaneous failure of locked faults. In contrast, slow-slip events proceed so slowly that slip is limited and only low-frequency (or no) seismic waves radiate. We find that slow-slip phenomena are not unique to the depths (tens of kilometres) of subduction zone plate interfaces. They occur on faults in many settings, at numerous scales and owing to various loading processes, including landslides and glaciers. Taken together, the observations indicate that slowly slipping fault surfaces relax most of the accrued stresses through aseismic slip. Aseismic motion can trigger more rapid slip elsewhere on the fault that is sufficiently fast to generate seismic waves. The resulting radiation has characteristics ranging from those indicative of slow but seismic slip, to those typical of earthquakes. The mode of seismic slip depends on the inherent characteristics of the fault, such as the frictional properties. Slow-slip events have previously been classified as a distinct mode of fault slip compared with that seen in earthquakes. We conclude that instead, slip modes span a continuum and are of common occurrence.

Nature Geoscience↗
USGS2010

Groundwater hydrology--coastal flow

How groundwater flow varies when long-term external conditions change is little documented. Geochemical evidence shows that sea-level rise at the end of the last glacial period led to a shift in the flow patterns of coastal groundwater beneath Florida.

Florida↗
USGS2010

Broad accommodation of rift-related extension recorded by dyke intrusion in Saudi Arabia

The extensive harrat lava province of Arabia formed during the past 30 million years in response to Red Sea rifting and mantle upwelling. The area was regarded as seismically quiet, but between April and June 2009 a swarm of more than 30,000 earthquakes struck one of the lava fields in the province, Harrat Lunayyir, northwest Saudi Arabia. Concerned that larger damaging earthquakes might occur, the Saudi Arabian government evacuated 40,000 people from the region. Here we use geologic, geodetic and seismic data to show that the earthquake swarm resulted from magmatic dyke intrusion. We document a surface fault rupture that is 8 km long with 91 cm of offset. Surface deformation is best modelled by the shallow intrusion of a north-west trending dyke that is about 10 km long. Seismic waves generated during the earthquakes exhibit overlapping very low- and high-frequency components. We interpret the low frequencies to represent intrusion of magma and the high frequencies to represent fracturing of the crystalline basement rocks. Rather than extension being accommodated entirely by the central Red Sea rift axis, we suggest that the broad deformation observed in Harrat Lunayyir indicates that rift margins can remain as active sites of extension throughout rifting. Our analyses allowed us to forecast the likelihood of a future eruption or large earthquake in the region and informed the decisions made by the Saudi Arabian government to return the evacuees.

Nature Geoscience↗
USGS2010

High tsunami frequency as a result of combined strike-slip faulting and coastal landslides

Earthquakes on strike-slip faults can produce devastating natural hazards. However, because they consist predominantly of lateral motion, these faults are rarely associated with significant uplift or tsunami generation. And although submarine slides can generate tsunami, only a few per cent of all tsunami are believed to be triggered in this way. The 12 January Mw 7.0 Haiti earthquake exhibited primarily strike-slip motion but nevertheless generated a tsunami. Here we present data from a comprehensive field survey that covered the onshore and offshore area around the epicentre to document that modest uplift together with slope failure caused tsunamigenesis. Submarine landslides caused the most severe tsunami locally. Our analysis suggests that slide-generated tsunami occur an order-of-magnitude more frequently along the Gonave microplate than global estimates predict. Uplift was generated because of the earthquake?s location, where the Caribbean and Gonave microplates collide obliquely. The earthquake also caused liquefaction at several river deltas that prograde rapidly and are prone to failure. We conclude that coastal strike-slip fault systems such as the Enriquillog-Plantain Garden fault produce relief conducive to rapid sedimentation, erosion and slope failure, so that even modest predominantly strike-slip earthquakes can cause potentially catastrophic slide-generated tsunamig-a risk that is underestimated at present. ?? 2010 Macmillan Publishers Limited. All rights reserved.

Nature Geoscience↗
USGS2010

Complex rupture during the 12 January 2010 Haiti earthquake

Initially, the devastating Mw 7.0, 12 January 2010 Haiti earthquake seemed to involve straightforward accommodation of oblique relative motion between the Caribbean and North American plates along the Enriquillog-Plantain Garden fault zone. Here, we combine seismological observations, geologic field data and space geodetic measurements to show that, instead, the rupture process may have involved slip on multiple faults. Primary surface deformation was driven by rupture on blind thrust faults with only minor, deep, lateral slip along or near the main Enriquillog-Plantain Garden fault zone; thus the event only partially relieved centuries of accumulated left-lateral strain on a small part of the plate-boundary system. Together with the predominance of shallow off-fault thrusting, the lack of surface deformation implies that remaining shallow shear strain will be released in future surface-rupturing earthquakes on the Enriquillog-Plantain Garden fault zone, as occurred in inferred Holocene and probable historic events. We suggest that the geological signature of this earthquakeg-broad warping and coastal deformation rather than surface rupture along the main fault zoneg-will not be easily recognized by standard palaeoseismic studies. We conclude that similarly complex earthquakes in tectonic environments that accommodate both translation and convergenceg-such as the San Andreas fault through the Transverse Ranges of Californiag-may be missing from the prehistoric earthquake record. ?? 2010 Macmillan Publishers Limited. All rights reserved.

Nature Geoscience↗
USGS2010

Episodic swell growth inferred from variable uplift of the Cape Verde hotspot islands

On the Beagle voyage, Charles Darwin first noted the creation and subsidence of ocean islands 1 , establishing in geology’s infancy that island freeboard changes with time. Hotspot ocean islands have an obvious mechanism for freeboard change through the growth of the bathymetric anomaly, or swell 2 , on which the islands rest. Models for swell development indicate that flexural 9 , thermal 2 , 3 or dynamic pressure 4 , 5 , 6 , 8 contributions, as well as spreading of melt residue from the hotspot 7 , can all contribute to island uplift. Here we test various models for swell development using the uplift histories for the islands of the Cape Verde hotspot, derived from isotopic dating of marine terraces and subaerial to submarine lava-flow morphologies. The island uplift histories, in conjunction with inter-island spacing, uplift rate and timing differences, rule out flexural, thermal or dynamic pressure contributions. We also find that uplift cannot be reconciled with models that advocate the spreading of melt residue in swell development unless swell growth is episodic. Instead, we infer from the uplift histories that two processes have acted to raise the islands during the past 6 Myr. During an initial phase, mantle processes acted to build the swell. Subsequently, magmatic intrusions at the island edifice caused 350 m of local uplift at the scale of individual islands. Finally, swell-wide uplift contributed a further 100 m of surface rise.

Nature Geoscience↗
USGS2010

Localized damage associated with topographic amplification during the 12 January 2010 M 7.0 Haiti earthquake

Local geological conditions, including both near-surface sedimentary layers 1 , 2 , 3 , 4 and topographic features 5 , 6 , 7 , 8 , 9 , are known to significantly influence ground motions caused by earthquakes. Microzonation maps use local geological conditions to characterize seismic hazard, but commonly incorporate the effect of only sedimentary layers 10 , 11 , 12 . Microzonation does not take into account local topography, because significant topographic amplification is assumed to be rare. Here we show that, although the extent of structural damage in the 2010 Haiti earthquake was primarily due to poor construction, topographic amplification contributed significantly to damage in the district of Petionville, south of central Port-au-Prince. A large number of substantial, relatively well-built structures situated along a foothill ridge in this district sustained serious damage or collapse. Using recordings of aftershocks, we calculate the ground motion response at two seismic stations along the topographic ridge and at two stations in the adjacent valley. Ground motions on the ridge are amplified relative to both sites in the valley and a hard-rock reference site, and thus cannot be explained by sediment-induced amplification. Instead, the amplitude and predominant frequencies of ground motion indicate the amplification of seismic waves by a narrow, steep ridge. We suggest that microzonation maps can potentially be significantly improved by incorporation of topographic effects.

Nature Geoscience↗
USGS2023

Importance of subsurface water for hydrological response during storms in a post-wildfire bedrock landscape

Wildfire alters the hydrologic cycle, with important implications for water supply and hazards including flooding and debris flows. In this study we use a combination of electrical resistivity and stable water isotope analyses to investigate the hydrologic response during storms in three catchments: one unburned and two burned during the 2020 Bobcat Fire in the San Gabriel Mountains, California, USA. Electrical resistivity imaging shows that in the burned catchments, rainfall infiltrated into the weathered bedrock and persisted. Stormflow isotope data indicate that the amount of mixing of surface and subsurface water during storms was similar in all catchments, despite higher streamflow post-fire. Therefore, both surface runoff and infiltration likely increased in tandem. These results suggest that the hydrologic response to storms in post-fire environments is dynamic and involves more surface-subsurface exchange than previously conceptualized, which has important implications for vegetation regrowth and post-fire landslide hazards for years following wildfire.

California↗
USGS2017

Granular flows at recurring slope lineae on Mars indicate a limited role for liquid water

Recent liquid water flow on Mars has been proposed based on geomorphological features, such as gullies. Recurring slope lineae — seasonal flows that are darker than their surroundings — are candidate locations for seeping liquid water on Mars today, but their formation mechanism remains unclear. Topographical analysis shows that the terminal slopes of recurring slope lineae match the stopping angle for granular flows of cohesionless sand in active Martian aeolian dunes. In Eos Chasma, linea lengths vary widely and are longer where there are more extensive angle-of-repose slopes, inconsistent with models for water sources. These observations suggest that recurring slope lineae are granular flows. The preference for warm seasons and the detection of hydrated salts are consistent with some role for water in their initiation. However, liquid water volumes may be small or zero, alleviating planetary protection concerns about habitable environments.

Nature Geoscience↗
USGS2018

Corrugated megathrust revealed offshore from Costa Rica

Exhumed faults are rough, often exhibiting topographic corrugations oriented in the direction of slip; such features are fundamental to mechanical processes that drive earthquakes and fault evolution. However, our understanding of corrugation genesis remains limited due to a lack of in situ observations at depth, especially at subducting plate boundaries. Here we present three-dimensional seismic reflection data of the Costa Rica subduction zone that image a shallow megathrust fault characterized by corrugated, and chaotic and weakly corrugated topographies. The corrugated surfaces extend from near the trench to several kilometres down-dip, exhibit high reflection amplitudes (consistent with high fluid content/pressure) and trend 11–18° oblique to subduction, suggesting 15 to 25 mm yr − 1 of trench-parallel slip partitioning across the plate boundary. The corrugations form along portions of the megathrust with greater cumulative slip and may act as fluid conduits. In contrast, weakly corrugated areas occur adjacent to active plate bending faults where the megathrust has migrated up-section, forming a nascent fault surface. The variations in megathrust roughness imaged here suggest that abandonment and then reestablishment of the megathrust up-section transiently increases fault roughness. Analogous corrugations may exist along significant portions of subduction megathrusts globally.

Nature Geoscience↗
USGS2018

Dryland photoautotrophic soil surface communities endangered by global change

Photoautotrophic surface communities forming biological soil crusts (biocrusts) are crucial for soil stability as well as water, nutrient and trace gas cycling at regional and global scales. Quantitative information on their global coverage and the environmental factors driving their distribution patterns, however, are not readily available. We use observations and environmental modelling to estimate the global distribution of biocrusts and their response to global change using future projected scenarios. We find that biocrusts currently covering approximately 12% of Earth’s terrestrial surface will decrease by about 25–40% within 65 years due to anthropogenically caused climate change and land-use intensification, responding far more drastically than vascular plants. Our results illustrate that current biocrust occurrence is mainly driven by a combination of precipitation, temperature and land management, and future changes are expected to be affected by land-use and climate change in similar proportion. The predicted loss of biocrusts may substantially reduce the microbial contribution to nitrogen cycling and enhance the emissions of soil dust, which affects the functioning of ecosystems as well as human health and should be considered in the modelling, mitigation and management of global change.

Nature Geoscience↗
USGS2018

An updated stress map of the continental U.S. reveals heterogeneous intraplate stress

Knowledge of the state of stress in the Earth’s crust is key to understanding the forces and processes responsible for earthquakes. Historically, low rates of natural seismicity in the central and eastern United States have complicated efforts to understand intraplate stress, but recent improvements in seismic networks and the spread of human-induced seismicity have greatly improved data coverage. Here we compile a nationwide stress map based on formal inversions of focal mechanisms that challenges the idea that deformation in continental interiors is driven primarily by broad, uniform stress fields derived from distant plate boundaries. Despite plate-boundary compression, extension dominates roughly half of the continent, and second-order forces related to lithospheric structure appear to control extension directions. We also show that the states of stress in several active eastern United States seismic zones differ significantly from surrounding areas and that these anomalies cannot be explained by transient processes, suggesting that earthquakes are focused by persistent, locally-derived sources of stress. Such spatially variable intraplate stress appears to justify the current, spatially variable estimates of seismic hazard. Future work to quantify sources of stress, stressing-rate magnitudes, and their relationship with strain and earthquake rates could allow prospective mapping of intraplate hazard.

Continental United States↗
USGS2018

Flushing of the deep Pacific Ocean and the deglacial rise of atmospheric CO2 concentrations

During the last deglaciation (19,000–9,000 years ago), atmospheric CO 2 increased by about 80 ppm. Understanding the mechanisms responsible for this change is a central theme of palaeoclimatology, relevant for predicting future CO 2 transfers in a warming world. Deglacial CO 2 rise hypothetically tapped an accumulated deep Pacific carbon reservoir, but the processes remain elusive as they are underconstrained by existing tracers. Here we report high-resolution authigenic neodymium isotope data in North Pacific sediment cores and infer abyssal Pacific overturning weaker than today during the Last Glacial Maximum but intermittently stronger during steps of deglacial CO 2 rise. Radiocarbon evidence suggestive of relatively ‘old’ deglacial deep Pacific water is reinterpreted here as an increase in preformed 14 C age of subsurface waters sourced near Antarctica, consistent with movement of aged carbon out of the deep ocean and release of CO 2 to the atmosphere during the abyssal flushing events. The timing of neodymium isotope changes suggests that deglacial acceleration of Pacific abyssal circulation tracked Southern Hemisphere warming, sea-ice retreat and increase of mean ocean temperature. The inferred magnitude of circulation changes is consistent with deep Pacific flushing as a significant, and perhaps dominant, control of the deglacial rise of atmospheric CO 2 .

Nature Geoscience↗
USGS2018

Crustal inheritance and a top-down control on arc magmatism at Mount St Helens

In a subduction zone, the volcanic arc marks the location where magma, generated via flux melting in the mantle wedge, migrates through the crust and erupts. While the location of deep magma broadly defines the arc position, here we argue that crustal structures, identified in geophysical data from the Washington Cascades magmatic arc, are equally important in controlling magma ascent and defining the spatial distribution and compositional variability of erupted material. As imaged by a three-dimensional resistivity model, a broad lower-crustal mush zone containing 3–10% interconnected melt underlies this segment of the arc, interpreted to episodically feed upper-crustal magmatic systems and drive eruptions. Mount St Helens is fed by melt channelled around a mid-Tertiary batholith also imaged in the resistivity model and supported by potential–field data. Regionally, volcanism and seismicity are almost exclusive of the batholith, while at Mount St Helens, along its margin, the ascent of viscous felsic melt is enabled by deep-seated metasedimentary rocks. Both the anomalous forearc location and composition of St Helens magmas are products of this zone of localized extension along the batholith margin. This work is a compelling example of inherited structural control on local stress state and magmatism.

Washington↗