Geology topics

Daniel E. McNamara

Publications and source records attributed to Daniel E. McNamara.

At least 37 records · Page 2Linked to original sources

USGS2016

A rare moderate‐sized (Mw 4.9) earthquake in Kansas: Rupture process of the Milan, Kansas, earthquake of 12 November 2014 and its relationship to fluid injection

The largest recorded earthquake in Kansas occurred northeast of Milan on 12 November 2014 ( M w 4.9) in a region previously devoid of significant seismic activity. Applying multistation processing to data from local stations, we are able to detail the rupture process and rupture geometry of the mainshock, identify the causative fault plane, and delineate the expansion and extent of the subsequent seismic activity. The earthquake followed rapid increases of fluid injection by multiple wastewater injection wells in the vicinity of the fault. The source parameters and behavior of the Milan earthquake and foreshock–aftershock sequence are similar to characteristics of other earthquakes induced by wastewater injection into permeable formations overlying crystalline basement. This earthquake also provides an opportunity to test the empirical relation that uses felt area to estimate moment magnitude for historical earthquakes for Kansas.

Seismological Research Letters↗

USGS2016

RMT focal plane sensitivity to seismic network geometry and faulting style

Modern tectonic studies often use regional moment tensors (RMTs) to interpret the seismotectonic framework of an earthquake or earthquake sequence; however, despite extensive use, little existing work addresses RMT parameter uncertainty. Here, we quantify how network geometry and faulting style affect RMT sensitivity. We examine how data-model fits change with fault plane geometry (strike and dip) for varying station configurations. We calculate the relative data fit for incrementally varying geometries about a best-fitting solution, applying our workflow to real and synthetic seismograms for both real and hypothetical station distributions and earthquakes. Initially, we conduct purely observational tests, computing RMTs from synthetic seismograms for hypothetical earthquakes and a series of well-behaved network geometries. We then incorporate real data and station distributions from the International Maule Aftershock Deployment (IMAD), which recorded aftershocks of the 2010 M W 8.8 Maule earthquake, and a set of regional stations capturing the ongoing earthquake sequence in Oklahoma and southern Kansas. We consider RMTs computed under three scenarios: (1) real seismic records selected for high data quality; (2) synthetic seismic records with noise computed for the observed source-station pairings and (3) synthetic seismic records with noise computed for all possible station-source pairings. To assess RMT sensitivity for each test, we observe the ‘fit falloff’, which portrays how relative fit changes when strike or dip varies incrementally; we then derive the ranges of acceptable strikes and dips by identifying the span of solutions with relative fits larger than 90 per cent of the best fit. For the azimuthally incomplete IMAD network, Scenario 3 best constrains fault geometry, with average ranges of 45° and 31° for strike and dip, respectively. In Oklahoma, Scenario 3 best constrains fault dip with an average range of 46°; however, strike is best constrained by Scenario 1, with a range of 26°. We draw two main conclusions from this study. (1) Station distribution impacts our ability to constrain RMTs using waveform time-series; however, in some tectonic settings, faulting style also plays a significant role and (2) increasing station density and data quantity (both the number of stations and the number of individual channels) does not necessarily improve RMT constraint. These results may be useful when organizing future seismic deployments (e.g. by concentrating stations in alignment with anticipated nodal planes), and in computing RMTs, either by guiding a more rigorous data selection process for input data or informing variable weighting among the selected data (e.g. by eliminating the transverse component when strike-slip mechanisms are expected).

Geophysical Journal International↗

USGS2015

Quantifying 10 years of improved earthquake-monitoring performance in the Caribbean region

Over 75 tsunamis have been documented in the Caribbean and adjacent regions during the past 500 years. Since 1500, at least 4484 people are reported to have perished in these killer waves. Hundreds of thousands are currently threatened along the Caribbean coastlines. Were a great tsunamigenic earthquake to occur in the Caribbean region today, the effects would potentially be catastrophic due to an increasingly vulnerable region that has seen significant population increases in the past 40–50 years and currently hosts an estimated 500,000 daily beach visitors from North America and Europe, a majority of whom are not likely aware of tsunami and earthquake hazards. Following the magnitude 9.1 Sumatra–Andaman Islands earthquake of 26 December 2004, the United Nations Educational, Scientific and Cultural Organization (UNESCO) Intergovernmental Coordination Group (ICG) for the Tsunami and other Coastal Hazards Early Warning System for the Caribbean and Adjacent Regions (CARIBE‐EWS) was established and developed minimum performance standards for the detection and analysis of earthquakes. In this study, we model earthquake‐magnitude detection threshold and P‐wave detection time and demonstrate that the requirements established by the UNESCO ICG CARIBE‐EWS are met with 100% of the network operating. We demonstrate that earthquake‐monitoring performance in the Caribbean Sea region has improved significantly in the past decade as the number of real‐time seismic stations available to the National Oceanic and Atmospheric Administration tsunami warning centers have increased. We also identify weaknesses in the current international network and provide guidance for selecting the optimal distribution of seismic stations contributed from existing real‐time broadband national networks in the region.

Seismological Research Letters↗

USGS2015

Rapid characterization of the 2015 M w 7.8 Gorkha, Nepal, earthquake sequence and its seismotectonic context

Earthquake response and related information products are important for placing recent seismic events into context and particularly for understanding the impact earthquakes can have on the regional community and its infrastructure. These tools are even more useful if they are available quickly, ahead of detailed information from the areas affected by such earthquakes. Here we provide an overview of the response activities and related information products generated and provided by the U.S. Geological Survey National Earthquake Information Center in association with the 2015 M 7.8 Gorkha, Nepal, earthquake. This group monitors global earthquakes 24  hrs/day and 7  days/week to provide rapid information on the location and size of recent events and to characterize the source properties, tectonic setting, and potential fatalities and economic losses associated with significant earthquakes. We present the timeline over which these products became available, discuss what they tell us about the seismotectonics of the Gorkha earthquake and its aftershocks, and examine how their information is used today, and might be used in the future, to help mitigate the impact of such natural disasters.

Seismological Research Letters↗

USGS2015

Strong-motion observations of the M 7.8 Gorkha, Nepal, earthquake sequence and development of the N-shake strong-motion network

We present and describe strong-motion data observations from the 2015 M 7.8 Gorkha, Nepal, earthquake sequence collected using existing and new Quake-Catcher Network (QCN) and U.S. Geological Survey NetQuakes sensors located in the Kathmandu Valley. A comparison of QCN data with waveforms recorded by a conventional strong-motion (NetQuakes) instrument validates the QCN data. We present preliminary analysis of spectral accelerations, and peak ground acceleration and velocity for earthquakes up to M 7.3 from the QCN stations, as well as preliminary analysis of the mainshock recording from the NetQuakes station. We show that mainshock peak accelerations were lower than expected and conclude the Kathmandu Valley experienced a pervasively nonlinear response during the mainshock. Phase picks from the QCN and NetQuakes data are also used to improve aftershock locations. This study confirms the utility of QCN instruments to contribute to ground-motion investigations and aftershock response in regions where conventional instrumentation and open-access seismic data are limited. Initial pilot installations of QCN instruments in 2014 are now being expanded to create the Nepal–Shaking Hazard Assessment for Kathmandu and its Environment (N-SHAKE) network.

Seismological Research Letters↗

USGS2015

Reactivated faulting near Cushing, Oklahoma: Increased potential for a triggered earthquake in an area of United States strategic infrastructure

In October 2014 two moderate-sized earthquakes ( Mw 4.0 and 4.3) struck south of Cushing, Oklahoma, below the largest crude oil storage facility in the world. Combined analysis of the spatial distribution of earthquakes and regional moment tensor focal mechanisms indicate reactivation of a subsurface unnamed and unmapped left-lateral strike-slip fault. Coulomb failure stress change calculations using the relocated seismicity and slip distribution determined from regional moment tensors, allow for the possibility that the Wilzetta-Whitetail fault zone south of Cushing, Oklahoma, could produce a large, damaging earthquake comparable to the 2011 Prague event. Resultant very strong shaking levels (MMI VII) in the epicentral region present the possibility of this potential earthquake causing moderate to heavy damage to national strategic infrastructure and local communities.

Oklahoma↗

USGS2015

Hundreds of earthquakes per day: The 2014 Guthrie, Oklahoma, Earthquake Sequence

A remarkable increase in seismic activity in Oklahoma since 2009 has been shown to correlate closely with enhanced hydrocarbon extraction and associated wastewater disposal; 99% of this recent Oklahoma earthquake activity has occurred within 15 km of a call II injection well (Ellsworth, 2013). In response to this increase in seismic activity, the U.S. Geological Survey (USGS) partnered with the Oklahoma Geological Survey (OGS) to exchange waveform data from permanent and temporary seismic stations to improve the cataloging of earthquake source parameters for a broad region of north-central Oklahoma. For a particularly persistent earthquake sequence near Guthrie, Oklahoma, a subspace detection method is applied to data from nearby seismic stations. This approach documents the occurrence of hundreds of readily detectable, highly similar, earthquakes per day, with rates occasionally exceeding 1000 earthquakes per day. Time-varying changes in b-value appear episodic, suggesting a correlation with periods of reversible fault weakening and associated failure.

Oklahoman↗

USGS2015

Earthquake hypocenters and focal mechanisms in central Oklahoma reveal a complex system of reactivated subsurface strike-slip faulting

The sharp increase in seismicity over a broad region of central Oklahoma has raised concern regarding the source of the activity and its potential hazard to local communities and energy industry infrastructure. Since early 2010, numerous organizations have deployed temporary portable seismic stations in central Oklahoma in order to record the evolving seismicity. In this study, we apply a multiple-event relocation method to produce a catalog of 3,639 central Oklahoma earthquakes from late 2009 through 2014. RMT source parameters were determined for 195 of the largest and best-recorded earthquakes. Combining RMT results with relocated seismicity enabled us to determine the length, depth and style-of-faulting occurring on reactivated subsurface fault systems. Results show that the majority of earthquakes occur on near vertical, optimally oriented (NE-SW and NW-SE), strike-slip faults in the shallow crystalline basement. These are necessary first order observations required to assess the potential hazards of individual faults in Oklahoma.

Oklahoma↗

USGS2015

The 2011 Virginia M5.8 earthquake: Insights from seismic reflection imaging into the influence of older structures on eastern U.S. seismicity

The Mineral, Virginia (USA), earthquake of 23 August 2011 occurred at 6– 8 km depth within the allochthonous terranes of the Appalachian Piedmont Province, rupturing an ~N36°E striking reverse fault dipping ~50° southeast. This study used the Interstate Highway 64 seismic refl ection profi le acquired ~6 km southwest of the hypocenter to examine the structural setting of the earthquake. The profi le shows that the 2011 earthquake and its aftershocks are almost entirely within the early Paleozoic Chopawamsic volcanic arc terrane, which is bounded by listric thrust faults dipping 30°–40° southeast that sole out into an ~2-km-thick, strongly refl ective zone at 7– 12 km depth. Refl ectors above and below the southward projection of the 2011 earthquake focal plane do not show evidence for large displacement, and the updip projection of the fault plane does not match either the location or trend of a previously mapped fault or lithologic boundary. The 2011 earthquake thus does not appear to be a simple reactivation of a known Paleozoic thrust fault or a major Mesozoic rift basin-boundary fault. The fault that ruptured appears to be a new fault, a fault with only minor displacement, or to not extend the ~3 km from the aftershock zone to the seismic profi le. Although the Paleozoic structures appear to infl uence the general distribution of seismicity in the area, Central Virginia seismic zone earthquakes have yet to be tied directly to specifi c fault systems mapped at the surface or imaged on seismic profiles.

Virginia↗

USGS2015

Aftershocks illuminate the 2011 Mineral, Virginia, earthquake causative fault zone and nearby active faults

Deployment of temporary seismic stations after the 2011 Mineral, Virginia (USA), earthquake produced a well-recorded aftershock sequence. The majority of aftershocks are in a tabular cluster that delineates the previously unknown Quail fault zone. Quail fault zone aftershocks range from ~3 to 8 km in depth and are in a 1-km-thick zone striking ~036° and dipping ~50°SE, consistent with a 028°, 50°SE main-shock nodal plane having mostly reverse slip. This cluster extends ~10 km along strike. The Quail fault zone projects to the surface in gneiss of the Ordovician Chopawamsic Formation just southeast of the Ordovician–Silurian Ellisville Granodiorite pluton tail. The following three clusters of shallow (<3 km) aftershocks illuminate other faults. (1) An elongate cluster of early aftershocks, ~10 km east of the Quail fault zone, extends 8 km from Fredericks Hall, strikes ~035°–039°, and appears to be roughly vertical. The Fredericks Hall fault may be a strand or splay of the older Lakeside fault zone, which to the south spans a width of several kilometers. (2) A cluster of later aftershocks ~3 km northeast of Cuckoo delineates a fault near the eastern contact of the Ordovician Quantico Formation. (3) An elongate cluster of late aftershocks ~1 km northwest of the Quail fault zone aftershock cluster delineates the northwest fault (described herein), which is temporally distinct, dips more steeply, and has a more northeastward strike. Some aftershock-illuminated faults coincide with preexisting units or structures evident from radiometric anomalies, suggesting tectonic inheritance or reactivation.

Virginia↗

USGS2015

Efforts to monitor and characterize the recent increasing seismicity in central Oklahoma

The sharp increase in seismicity over a broad region of central Oklahoma has raised concerns regarding the source of the activity and its potential hazard to local communities and energy-industry infrastructure. Efforts to monitor and characterize the earthquake sequences in central Oklahoma are reviewed. Since early 2010, numerous organizations have deployed temporary portable seismic stations in central Oklahoma to record the evolving seismicity. A multiple-event relocation method is applied to produce a catalog of central Oklahoma earthquakes from late 2009 into early 2015. Regional moment tensor (RMT) source parameters were determined for the largest and best-recorded earthquakes. Combining RMT results with relocated seismicity enabled determination of the length, depth, and style of faulting occurring on reactivated subsurface fault systems. It was found that the majority of earthquakes occur on near-vertical, optimally oriented (northeast-southwest and northwest-southeast) strike-slip faults in the shallow crystalline basement. In 2014, 17 earthquakes occurred with magnitudes of 4 or larger. It is suggested that these recently reactivated fault systems pose the greatest potential hazard to the region.

Oklahoma↗

USGS2014

Frequency-dependent seismic attenuation in the eastern United States as observed from the 2011 central Virginia earthquake and aftershock sequence

Ground shaking due to earthquakes in the eastern United States (EUS) is felt at significantly greater distances than in the western United States (WUS) and for some earthquakes it has been shown to display a strong preferential direction. Shaking intensity variation can be due to propagation path effects, source directivity, and/or site amplification. In this paper, we use S and Lg waves recorded from the 2011 central Virginia earthquake and aftershock sequence, in the Central Virginia Seismic Zone, to quantify attenuation as frequency‐dependent Q ( f ). In support of observations based on shaking intensity, we observe high Q values in the EUS relative to previous studies in the WUS with especially efficient propagation along the structural trend of the Appalachian mountains. Our analysis of Q ( f ) quantifies the path effects of the northeast‐trending felt distribution previously inferred from the U.S. Geological Survey (USGS) “Did You Feel It” data, historic intensity data, and the asymmetrical distribution of rockfalls and landslides.

Bulletin of the Seismological Society of America↗

USGS2014

Ground-motion site effects from multimethod shear-wave velocity characterization at 16 seismograph stations deployed for aftershocks of the August 2011 Mineral, Virginia earthquake

We characterize shear-wave velocity versus depth (Vs profile) at 16 portable seismograph sites through the epicentral region of the 2011 M w 5.8 Mineral (Virginia, USA) earthquake to investigate ground-motion site effects in the area. We used a multimethod acquisition and analysis approach, where active-source horizontal shear (SH) wave reflection and refraction as well as active-source multichannel analysis of surface waves (MASW) and passive-source refraction microtremor (ReMi) Rayleigh wave dispersion were interpreted separately. The time-averaged shear-wave velocity to a depth of 30 m (Vs30), interpreted bedrock depth, and site resonant frequency were estimated from the best-fit Vs profile of each method at each location for analysis. Using the median Vs30 value (270–715 m/s) as representative of a given site, we estimate that all 16 sites are National Earthquake Hazards Reduction Program (NEHRP) site class C or D. Based on a comparison of simplified mapped surface geology to median Vs30 at our sites, we do not see clear evidence for using surface geologic units as a proxy for Vs30 in the epicentral region, although this may primarily be because the units are similar in age (Paleozoic) and may have similar bulk seismic properties. We compare resonant frequencies calculated from ambient noise horizontal:vertical spectral ratios (HVSR) at available sites to predicted site frequencies (generally between 1.9 and 7.6 Hz) derived from the median bedrock depth and average Vs to bedrock. Robust linear regression of HVSR to both site frequency and Vs30 demonstrate moderate correlation to each, and thus both appear to be generally representative of site response in this region. Based on Kendall tau rank correlation testing, we find that Vs30 and the site frequency calculated from average Vs to median interpreted bedrock depth can both be considered reliable predictors of weak-motion site effects in the epicentral region.

Virginia↗

USGS2014

Site response in the eastern United States: A comparison of Vs30 measurements with estimates from horizontal:vertical spectral ratios

Earthquake damage is often increased due to local ground-motion amplification caused by soft soils, thick basin sediments, topographic effects, and liquefaction. A critical factor contributing to the assessment of seismic hazard is detailed information on local site response. In order to address and quantify the site response at seismograph stations in the eastern United States, we investigate the regional spatial variation of horizontal:vertical spectral ratios (HVSR) using ambient noise recorded at permanent regional and national network stations as well as temporary seismic stations deployed in order to record aftershocks of the 2011 Mineral, Virginia, earthquake. We compare the HVSR peak frequency to surface measurements of the shear-wave seismic velocity to 30 m depth (Vs30) at 21 seismograph stations in the eastern United States and find that HVSR peak frequency increases with increasing Vs30. We use this relationship to estimate the National Earthquake Hazards Reduction Program soil class at 218 ANSS (Advanced National Seismic System), GSN (Global Seismographic Network), and RSN (Regional Seismograph Networks) locations in the eastern United States, and suggest that this seismic station–based HVSR proxy could potentially be used to calibrate other site response characterization methods commonly used to estimate shaking hazard.

GSA Special Papers↗

USGS2014

Seismicity of the Earth 1900-2013 offshore British Columbia-southeastern Alaska and vicinity

The tectonics of the Pacific margin of North America between Vancouver Island and south-central Alaska are dominated by the northwest motion of the Pacific plate with respect to the North America plate at a velocity of approximately 50 mm/yr. In the south of this mapped region, convergence between the northern extent of the Juan de Fuca plate (also known as the Explorer microplate) and North America plate dominate. North from the Explorer, Pacific, and North America plate triple junction, Pacific:North America motion is accommodated along the ~650-km-long Queen Charlotte fault system. Offshore of Haida Gwaii and to the southwest, the obliquity of the Pacific:North America plate motion vector creates a transpressional regime, and a complex mixture of strike-slip and convergent (underthrusting) tectonics. North of the Haida Gwaii islands, plate motion is roughly parallel to the plate boundary, resulting in almost pure dextral strike-slip motion along the Queen Charlotte fault. To the north, the Queen Charlotte fault splits into multiple structures, continuing offshore of southwestern Alaska as the Fairweather fault, and branching east into the Chatham Strait and Denali faults through the interior of Alaska. The plate boundary north and west of the Fairweather fault ultimately continues as the Alaska-Aleutians subduction zone, where Pacific plate lithosphere subducts beneath the North America plate at the Aleutians Trench. The transition is complex, and involves intraplate structures such as the Transition fault. The Pacific margin offshore British Columbia is one of the most active seismic zones in North America and has hosted a number of large earthquakes historically.

Alaska, British Columbia↗

USGS2014

Seismicity of the Earth 1900-2013 East African Rift

The East African Rift system (EARS) is a 3,000-km-long Cenozoic age continental rift extending from the Afar triple junction, between the horn of Africa and the Middle East, to western Mozambique. Sectors of active extension occur from the Indian Ocean, west to Botswana and the Democratic Republic of the Congo (DRC). It is the only rift system in the world that is active on a continent-wide scale, providing geologists with a view of how continental rifts develop over time into oceanic spreading centers like the Mid-Atlantic Ridge. Rifting in East Africa is not all coeval; volcanism and faulting have been an ongoing phenomenon on the continent since the Eocene (~45 Ma). The rifting began in northern East Africa, and led to the separation of the Nubia (Africa) and Arabia plates in the Red Sea and Gulf of Aden, and in the Lake Turkana area at the Kenya-Ethiopia border. A Paleogene mantle superplume beneath East Africa caused extension within the Nubia plate, as well as a first order topographic high known as the African superswell which now includes most of the eastern and southern sectors of the Nubia plate. Widespread volcanism erupted onto much of the rising plateau in Ethiopia during the Eocene-Oligocene (45–29 Ma), with chains of volcanoes forming along the rift separating Africa and Arabia. Since the initiation of rifting in northeastern Africa, the system has propagated over 3,000 km to the south and southwest, and it experiences seismicity as a direct result of the extension and active magmatism.

Open-File Report↗

USGS2013

The Mw 5.8 Mineral, Virginia, earthquake of August 2011 and aftershock sequence: constraints on earthquake source parameters and fault geometry

The M w 5.8 earthquake of 23 August 2011 (17:51:04 UTC) (moment, M0 5.7×10 17 N·m) occurred near Mineral, Virginia, within the central Virginia seismic zone and was felt by more people than any other earthquake in United States history. The U.S. Geological Survey (USGS) received 148,638 felt reports from 31 states and 4 Canadian provinces. The USGS PAGER system estimates as many as 120,000 people were exposed to shaking intensity levels of IV and greater, with approximately 10,000 exposed to shaking as high as intensity VIII. Both regional and teleseismic moment tensor solutions characterize the earthquake as a northeast‐striking reverse fault that nucleated at a depth of approximately 7±2 km. The distribution of reported macroseismic intensities is roughly ten times the area of a similarly sized earthquake in the western United States (Horton and Williams, 2012). Near‐source and far‐field damage reports, which extend as far away as Washington, D.C., (135 km away) and Baltimore, Maryland, (200 km away) are consistent with an earthquake of this size and depth in the eastern United States (EUS). Within the first few days following the earthquake, several government and academic institutions installed 36 portable seismograph stations in the epicentral region, making this among the best‐recorded aftershock sequences in the EUS. Based on modeling of these data, we provide a detailed description of the source parameters of the mainshock and analysis of the subsequent aftershock sequence for defining the fault geometry, area of rupture, and observations of the aftershock sequence magnitude–frequency and temporal distribution. The observed slope of the magnitude–frequency curve or b‐value for the aftershock sequence is consistent with previous EUS studies (b=0.75), suggesting that most of the accumulated strain was released by the mainshock. The aftershocks define a rupture that extends between approximately 2–8 km in depth and 8–10 km along the strike of the fault plane. Best‐fit modeling of the geometry of the aftershock sequence defines a rupture plane that strikes N36°E and dips to the east‐southeast at 49.5°. Moment tensor solutions of the mainshock and larger aftershocks are consistent with the distribution of aftershock locations, both indicating reverse slip along a northeast–southwest striking southeast‐dipping fault plane.

Virginia↗

USGS2013

Quantifying potential earthquake and tsunami hazard in the Lesser Antilles subduction zone of the Caribbean region

In this study, we quantify the seismic and tsunami hazard in the Lesser Antilles subduction zone, focusing on the plate interface offshore of Guadeloupe. We compare potential strain accumulated via GPS-derived plate motions to strain release due to earthquakes that have occurred over the past 110 yr, and compute the resulting moment deficit. Our results suggest that enough strain is currently stored in the seismogenic zone of the Lesser Antilles subduction arc in the region of Guadeloupe to cause a large and damaging earthquake of magnitude M w ∼ 8.2 ± 0.4. We model several scenario earthquakes over this magnitude range, using a variety of earthquake magnitudes and rupture areas, and utilizing the USGS ShakeMap and PAGER software packages. Strong ground shaking during the earthquake will likely cause loss of life and damage estimated to be in the range of several tens to several hundreds of fatalities and hundreds of millions to potentially billions of U.S. dollars of damage. In addition, such an event could produce a significant tsunami. Modelled tsunamis resulting from these scenario earthquakes predict meter-scale wave amplitudes even for events at the lower end of our magnitude range (M 7.8), and heights of over 3 m in several locations with our favoured scenario (M 8.0, partially locked interface from 15–45 km depth). In all scenarios, only short lead-times (on the order of tens of minutes) would be possible in the Caribbean before the arrival of damaging waves.

Lesser Antilles↗