Physical Sciences and Mathematics Commons^™

Dextral, Normal, And Sinistral Faulting Across The Eastern California Shear Zone-Mina Deflection Transition, California-Nevada, Usa, Kevin Delano, Jeffrey Lee, Rachelle Roper, Andrew Calvert

All Faculty Scholarship for the College of the Sciences

Strike-slip faults commonly include extensional and contractional bends and stepovers, whereas rotational stepovers are less common. The Volcanic Tableland, Black Mountain, and River Spring areas (California and Nevada, USA) (hereafter referred to as the VBR region) straddle the transition from the dominantly NW-striking dextral faults that define the northwestern part

of the eastern California shear zone into a rotational stepover characterized by dominantly NE-striking sinistral faults that define the southwestern Mina deflection. New detailed geologic mapping, structural studies, and 40Ar/39Ar geochronology across the VBR region allow us to calculate Pliocene to Pleistocene fault slip rates and test predictions for the …

Tidal And Spatial Variability Of Flow Speed And Seismicity Near The Grounding Zone Of Beardmore Glacier, Antarctica, Jade Cooley, J. Paul Winberry, Michelle Koutnik, Howard Conway

All Faculty Scholarship for the College of the Sciences

GPS measurements of tidal modulation of ice flow and seismicity within the grounding zone of Beardmore Glacier show that tidally induced fluctuations of horizontal flow are largest near the grounding line and decrease downstream. Seismic activity is continuous, but peaks occur on falling and rising tides. Beamforming methods reveal that most seismic events originate from two distinct locations, one on the grid-north side of the grounding zone, and one on the grid-south side. The broad pattern of deformation generated as Beardmore Glacier merges with the Ross Ice Shelf results in net extension along the grid-north side of the grounding zone …

Seismic Tremor Reveals Spatial Organization And Temporal Changes Of Subglacial Water System, Margot E. Vore, Timothy C. Bartholomaus, J. Paul Winberry, Jacob I. Walter, Jason M. Amundson

All Faculty Scholarship for the College of the Sciences

Subglacial water flow impacts glacier dynamics and shapes the subglacial environment. However, due to the challenges of observing glacier beds, the spatial organization of subglacial water systems and the time scales of conduit evolution and migration are largely unknown. To address these questions, we analyze 1.5‐ to 10‐Hz seismic tremor that we associate with subglacial water flow, hat is, glaciohydraulic tremor, at Taku Glacier, Alaska, throughout the 2016 melt season. We use frequency‐dependent polarization analysis to estimate glaciohydraulic tremor propagation direction (related to the subglacial conduit location) and a degree day melt model to monitor variations in melt‐water input. We …

The Crust And Upper Mantle Structure Of Central And West Antarctica From Bayesian Inversion Of Rayleigh Wave And Receiver Functions, Weisen Shen, Audrey D. Huerta, J. Paul Winberry

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We construct a new seismic model for central and West Antarctica by jointly inverting Rayleigh wave phase and group velocities along with P wave receiver functions. Ambient noise tomography exploiting data from more than 200 seismic stations deployed over the past 18 years is used to construct Rayleigh wave phase and group velocity dispersion maps. Comparison between the ambient noise phase velocity maps with those constructed using teleseismic earthquakes confirms the accuracy of both results. These maps, together with P receiver function waveforms, are used to construct a new 3-D shear velocity (Vs) model for the crust and uppermost mantle …

Slip Pulse And Resonance Of The Kathmandu Basin During The 2015 Gorkha Earthquake, Nepal, John Galetzka, Walter Szeliga

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Detailed geodetic imaging of earthquake ruptures enhances our understanding of earthquake physics and associated ground shaking. The 25 April 2015 moment magnitude 7.8 earthquake in Gorkha, Nepal was the first large continental megathrust rupture to have occurred beneath a high-rate (5-hertz) Global Positioning System (GPS) network. We used GPS and interferometric synthetic aperture radar data to model the earthquake rupture as a slip pulse ~20 kilometers in width, ~6 seconds in duration, and with a peak sliding velocity of 1.1 meters per second, which propagated toward the Kathmandu basin at ~3.3 kilometers per second over ~140 kilometers. The smooth slip …

The Mantle Transition Zone Beneath West Antarctica: Seismic Evidence For Hydration And Thermal Upwellings, E. L. Emry, A. A. Nyblade, J. Juliá, S. Anandakrishnan, R. C. Aster, D. A. Wiens, Audrey D. Huerta, T. J. Wilson

All Faculty Scholarship for the College of the Sciences

Although prior work suggests that a mantle plume is associated with Cenozoic rifting and volcanism in West Antarctica, the existence of a plume remains conjectural. Here we use P wave receiver functions (PRFs) from the Antarctic POLENET array to estimate mantle transition zone thickness, which is sensitive to temperature perturbations, throughout previously unstudied parts of West Antarctica. We obtain over 8000 high‐quality PRFs using an iterative, time domain deconvolution method filtered with a Gaussian width of 0.5 and 1.0, corresponding to frequencies less than ∼0.24 and ∼0.48 Hz, respectively. Single‐station and common conversion point stacks, migrated to depth using the …

Interseismic Strain Accumulation Along The Western Boundary Of The Indian Subcontinent, Walter Szeliga, Roger Bilham, Din Mohammad Kakar, Sarosh H. Lodi

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Despite an overall sinistral slip rate of ≈3 cm/yr, few major earthquakes have occurred in the past 200 years along the Chaman fault system, the western boundary of the India Plate with the Eurasia Plate. GPS and InSAR data reported here indicate sinistral shear velocities of 8–17 mm/yr across the westernmost branches of the fault system, suggesting that a significant fraction of the plate boundary slip is distributed in the fold and fault belt to the east. At its southernmost on‐land segment (≈26°N), near the triple junction between the Arabia, Eurasia, and India Plates, we find the velocity across the …

Surficial Slip Distribution On The Central Emerson Fault During The June 28, 1992, Landers Earthquake, California, Sally F. Mcgill, Charles M. Rubin

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We present the results of our mapping of a 5.6‐km length of the central Emerson fault that ruptured during the 1992 Landers earthquake in the southwestern Mojave Desert, California. The right‐lateral slip along this portion of the rupture varied from about 150 to 530 cm along the main rupture zone. In some locations a total of up to 110 cm of additional right‐lateral slip occurred on secondary faults up to 1.7 km away from the main rupture zone. Other secondary faults carried up to several tens of centimeters of left‐lateral or thrust displacement. The maximum net vertical displacement was 175 …

Long Dormancy, Low Slip Rate, And Similar Slip‐Per‐Event For The Emerson Fault, Eastern California Shear Zone, Charles M. Rubin, Kerry Sieh

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Excavations in a playa along the 1992 rupture of the Emerson fault reveal evidence of two paleoseismic events, with only one large prehistoric rupture in the past 15 millennia. Accelerator mass spectrometer radiocarbon ages of charcoal from playa sediments and from fault‐scarp colluvium directly beneath the playa beds indicate that the last large prehistoric slip event occurred about 9000 ka. Trench‐wall exposures revealed clear evidence of at least one pre‐9 ka rupture at the playa site. The event horizon of this earthquake is between two pedogenic carbonate layers that have radiocarbon ages of 14.8 ka and 24.1 ka, implying that …