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Lara S. Wagner

Publications and source records attributed to Lara S. Wagner.

3 recordsLinked to original sources

Ps-P tomography of a mid-crustal magma reservoir beneath Cleveland Volcano, Alaska

Seismic tomography of the crust is an essential tool for studying the three-dimensional structure of magmatic plumbing systems feeding active volcanoes, but it is often limited in resolution by the absence of deep local seismicity. Teleseismic receiver functions can be used to illuminate local structural variations, but typically do not account for the effects of three-dimensional velocity heterogeneities. Here we harness the complementary strengths of both techniques by processing Ps-P delay times derived from teleseismic receiver functions in a tomographic S wave inversion. Using our inversion technique, we produce the first tomographic crustal velocity model beneath Cleveland Volcano, identifying a vertically extensive high V P /V S anomaly beneath the volcano that likely signifies a middle-to-lower crustal magma reservoir. The observation is the first of its kind in the central Aleutians, illustrating the potential of our technique to advance our understanding of crustal magmatic systems without broad seismic networks or distributed local seismicity.

Alaska

Mw 4.2 Delaware Earthquake of 30 November 2017

The 30 November 2017 Delaware earthquake with magnitude MW 4.2 occurred beneath the northeastern tip of the Delmarva Peninsula near Dover, Delaware. The earthquake and its aftershocks provide an opportunity to evaluate seismicity in a passive margin setting using much improved coverage by high-quality permanent broadband seismometers at regional distance ranges in the central and eastern United States. This is the largest instrumentally recorded earthquake in Delaware and triggered a collaborative rapid-response effort by seismologists at five institutions along the mid-Atlantic. As a result of this effort, eighteen portable seismographs were deployed in the epicentral region within 24 hours of the mainshock. High-quality seismic recordings at over 380 permanent regional broadband seismographic stations in the eastern United States show a remarkably small decrease in amplitude with distance between 800-2000 km. The mainshock focal mechanism shows predominantly strike-slip motion with a significant thrust component. The orientation of the subhorizontal P-axis is consistent with that of earthquakes in the nearby Reading-Lancaster seismic zone in Pennsylvania, but are rotated counter-clockwise about 45º from that of the MW 5.8 Mineral, Virginia earthquake. We detected small aftershocks below the normal event detection threshold by using a waveform cross-correlation detection method. This demonstrated the effectiveness of this approach for earthquake studies and hazard evaluation in the eastern United States. Based on their waveform similarities, repeating earthquakes with magnitudes greater than 1.5 are detected in 2010, 2015, and 2017. While there is a large time interval between events, 5 years and 2.2 years respectively, the events occur within a spatially tight cluster located near the 2017 Dover DE earthquake mainshock.

Delaware

Tectonic evolution of the Central Andean Plateau and implications for the growth of plateaus

Current end-member models for the geodynamic evolution of orogenic plateaus predict ( a ) slow and steady rise during crustal shortening and ablative subduction (i.e., continuous removal) of the lower lithosphere or ( b ) rapid surface uplift following shortening, which is associated with punctuated removal of dense lower lithosphere and/or lower crustal flow. This review integrates results from recent studies of the modern lithospheric structure, geologic evolution, and surface uplift history of the Central Andean Plateau to evaluate the geodynamic processes involved in forming it. Comparison of the timing, magnitude, and distribution of shortening and surface uplift, in combination with other geologic evidence, highlights the pulsed nature of plateau growth. We discuss specific regions and time periods that show evidence for end-member geodynamic processes, including middle–late Miocene surface uplift of the southern Eastern Cordillera and Altiplano associated with shortening and ablative subduction, latest Oligocene–early Miocene and late Miocene–early Pliocene punctuated removal of dense lower lithosphere in the Eastern Cordillera and Altiplano, and late Miocene–early Pliocene crustal flow in the central and northern Altiplano.

Annual Review of Earth and Planetary Sciences