Stephen Hernández

Instituto Geofísico de la Escuela Politécnica Nacional

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Mario Ruiz

Instituto Geofísico de la Escuela Politécnica Nacional

Andrew Bell

University of Edinburgh

Patricia Mothes

Instituto Geofísico de la Escuela Politécnica Nacional

Jean‐Mathieu Nocquet

Géoazur

Silvana Hidalgo

Instituto Geofísico de la Escuela Politécnica Nacional

A. Meltzer

Lehigh University

Yvonne Font

Observatoire de la Côte d’Azur

F. Rolandone

Institut des Sciences de la Terre de Paris

Colton Lynner

University of Delaware

Philippe Charvis

Géoazur

Cooperative Institutions

Instituto Geofísico de la Escuela Politécnica Nacional

Centre National de la Recherche Scientifique

Institut de Recherche pour le Développement

Géoazur

Université Côte d'Azur

Observatoire de la Côte d’Azur

National Polytechnic School

Pennsylvania State University

United States Geological Survey

Planetary Science Institute

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Chronology and phenomenology of the 1982 and 2015 Wolf volcano eruptions, Galápagos Archipelago

Journal of Volcanology and Geothermal Research (2019)

Benjamin Bernard Michael J. Stock Diego Coppola Silvana Hidalgo Marco Bagnardi

Caldera

Effusive eruption

Archipelago

Lateral eruption

Scoria

Dense-rock equivalent

Lava field

Lava dome

10.1016/j.jvolgeores.2019.02.013

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Citations (21)

New insights on co- and post-seismic deformation and slip behavior associated with the Mw7.8 2016 Pedernales, Ecuador earthquake and its aftershock sequence

AGUFM (2017)

Lillian Soto-Cordero Jennifer L. Nealy A. Meltzer Hans Agurto‐Detzel A. P. Alvarado

Sequence (biology)

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Citations (1)

Upper mantle seismic anisotropy beneath the West Antarctic Rift System and surrounding region from shear wave splitting analysis

Geophysical Journal International (2014)

N. J. Accardo Douglas A. Wiens Stephen Hernández R. C. Aster A. Nyblade

We constrain azimuthal anisotropy in the West Antarctic upper mantle using shear wave splitting parameters obtained from teleseismic SKS, SKKS and PKS phases recorded at 37 broad-band seismometres deployed by the POLENET/ANET project. We use an eigenvalue technique to linearize the rotated and shifted shear wave horizontal particle motions and determine the fast direction and delay time for each arrival. High-quality measurements are stacked to determine the best fitting splitting parameters for each station. Overall, fast anisotropic directions are oriented at large angles to the direction of Antarctic absolute plate motion in both hotspot and no-net-rotation frameworks, showing that the anisotropy does not result from shear due to plate motion over the mantle. Further, the West Antarctic directions are substantially different from those of East Antarctica, indicating that anisotropy across the continent reflects multiple mantle regimes. We suggest that the observed anisotropy along the central Transantarctic Mountains (TAM) and adjacent West Antarctic Rift System (WARS), one of the largest zones of extended continental crust on Earth, results from asthenospheric mantle strain associated with the final pulse of western WARS extension in the late Miocene. Strong and consistent anisotropy throughout the WARS indicate fast axes subparallel to the inferred extension direction, a result unlike reports from the East African rift system and rifts within the Basin and Range, which show much greater variation. We contend that ductile shearing rather than magmatic intrusion may have been the controlling mechanism for accumulation and retention of such coherent, widespread anisotropic fabric. Splitting beneath the Marie Byrd Land Dome (MBL) is weaker than that observed elsewhere within the WARS, but shows a consistent fast direction, possibly representative of anisotropy that has been 'frozen-in' to remnant thicker lithosphere. Fast directions observed inland from the Amundsen Sea appear to be radial to the dome and may indicate radial horizontal mantle flow associated with an MBL plume head and low upper mantle velocities in this region, or alternatively to lithospheric features associated with the complex Cenozoic tectonics at the far-eastern end of the WARS.

Shear wave splitting

Seismic anisotropy

10.1093/gji/ggu117

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Citations (31)

Structural Control on Megathrust Rupture and Slip Behavior: Insights From the 2016 Mw 7.8 Pedernales Ecuador Earthquake

Journal of Geophysical Research Solid Earth (2020)

Lillian Soto-Cordero A. Meltzer Eric Bergman Mariah Hoskins Joshua C. Stachnik

Abstract The heterogeneous seafloor topography of the Nazca Plate as it enters the Ecuador subduction zone provides an opportunity to document the influence of seafloor roughness on slip behavior and megathrust rupture. The 2016 M w 7.8 Pedernales Ecuador earthquake was followed by a rich and active postseismic sequence. An internationally coordinated rapid response effort installed a temporary seismic network to densify coastal stations of the permanent Ecuadorian national seismic network. A combination of 82 onshore short and intermediate period and broadband seismic stations and six ocean bottom seismometers recorded the postseismic Pedernales sequence for over a year after the mainshock. A robust earthquake catalog combined with calibrated relocations for a subset of magnitude ≥4 earthquakes shows pronounced spatial and temporal clustering. A range of slip behavior accommodates postseismic deformation including earthquakes, slow slip events, and earthquake swarms. Models of plate coupling and the consistency of earthquake clustering and slip behavior through multiple seismic cycles reveal a segmented subduction zone primarily controlled by subducted seafloor topography, accreted terranes, and inherited structure. The 2016 Pedernales mainshock triggered moderate to strong earthquakes (5 ≤ M ≤ 7) and earthquake swarms north of the mainshock rupture close to the epicenter of the 1906 M w 8.8 earthquake and in the segment of the subduction zone that ruptured in 1958 in a M w 7.7 earthquake.

Seafloor Spreading

Epicenter

Seismometer

Slow earthquake

Earthquake rupture

10.1029/2019jb018001

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Citations (15)

Relationship between volcanic ash fallouts and seismic tremor: quantitative assessment of the 2015 eruptive period at Cotopaxi volcano, Ecuador

Bulletin of Volcanology (2016)

Benjamin Bernard Jean Battaglia Antonio Proaño Silvana Hidalgo Francisco J. Vasconez

Volcanic ash

Vulcanian eruption

10.1007/s00445-016-1077-5

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Citations (44)

Seismic Anisotropy of the Antarctic Upper Mantle from Shear Wave Splitting Analysis of POLENET and AGAP Seismograms

AGU Fall Meeting Abstracts (2009)

Stephen Hernández Douglas A. Wiens S. Anandakrishnan R. C. Aster A. D. Huerta

Seismogram

Shear wave splitting

Seismic anisotropy

Shear waves

Passive seismic

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Citations (3)

The rise and fall of periodic ‘drumbeat’ seismicity at Tungurahua volcano, Ecuador

Earth and Planetary Science Letters (2017)

Andrew Bell Stephen Hernández Elizabeth Gaunt Patricia Mothes Mario Ruiz

Lava dome

10.1016/j.epsl.2017.07.030

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Citations (37)

Geophysical Footprints of Cotopaxi’s Unrest and Minor Eruptions in 2015: An Opportunity to Test Scientific and Community Preparedness

Advances in volcanology (2017)

Patricia Mothes Mario Ruiz Edwin Viracucha Patricio Ramón Stephen Hernández

Cotopaxi volcano, Ecuador, experienced notable restlessness in 2015 that was a major deviation from its normal background activity. Starting in April and continuing through November 2015 strong seismic activity, infrasound registry, hikes in SO2 degassing and flank deformation with small displacements were some of the geophysical anomalies that were registered. Obvious superficial changes, such as small hydromagmatic eruptions, emission of vapor and ash columns, thermal hotspots around the crater and in nearby orifices and exacerbated glacier melting were also observed. Our contribution provides an overview of the 2015 Cotopaxi unrest by presenting the patterns of geophysical data and the sequence of events produced by the volcano. Cotopaxi’s last important VEI 4 eruption was in 1877. Then it had devastating effects because of the transit of huge lahars down 3 major drainages. Comparatively, the 2015 activity never surpassed a magnitude VEI 2 and principally produced limited hydromagmatic explosions and semi-continuous low energy emissions and light ashfalls. Given the potential of major destruction from a large Cotopaxi eruption it is important to understand the geophysical fingerprints that characterized the 2015 episode with an eye to identifying onset of future restless periods. Overall, the monitoring activities, the data interpretation, formulation of reasonable eruptive scenarios, and finally, the preparation of a stream of constant information being relayed to concerned authorities and the public, was a real test of the IGEPN’s capacity to deal with a complicated eruption situation whose outcome was not apparent at the beginning, but which concluded in a very small eruptive episode.

Unrest

Preparedness

Lahar

10.1007/11157_2017_10

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Citations (17)

Detailed Spatio-temporal Distribution of the 16 April 2016 M7.8 Pedernales Ecuador Aftershock Sequence

AGU Fall Meeting Abstracts (2016)

Stephen Hernández Yadira Silveira Font F. Rolandone Jean‐Mathieu Nocquet S. L. Beck

Sequence (biology)

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