Research

We use seismology and applied geophysics to study the Earth and how it changes. The depths of interest are usually somewhere between our feet and the base of the lithosphere.

Focus topics include:

Three-dimensional seismic perspective of shallow-most northern Hikurangi subduction zone with overlain P-wave velocities . The lower panel is cut on the top of the volcanic basement horizon. From Gase et al. 2023 - in Science Advances.

Subduction zones:

These tectonic plate boundaries generate hazardous earthquakes and tsunami and are the conveyor belts that transport water and rock from the Earth's outer surface to the mantle. In our most recent work, we use controlled source seismic imaging to map buried faults, sediments, and fluids within New Zealand's Hikurangi subduction zone. These results can be used to test whether fault structures and rock properties effect earthquakes and tsunami.

Select publications:

Subducting volcaniclastic-rich upper crust supplies fluids for shallow megathrust and slow slip (2023)

Hikurangi megathrust slip behavior influenced by lateral variability in sediment subduction (2022)

Crustal structure of the northern Hikurangi margin (2021)

Seismic reflection image of crustal sill complexes near Whakaari/White Island volcano. These sills may source volatiles that cause earthquake swarms (Aber et al., in prep).

Volcanic provinces

The internal structure of volcanic systems - where and how is magma stored and transported to the surface - is a mystery that influences eruptions and the geologic evolution of large regions of the earth, such as mid-ocean ridges, volcanic arcs, and large igneous provinces. We use marine seismic methods to construct images of magmatic plumbing systems and to view the insides of ancient volcanoes.

Select publications:

Volcanic structure of the western Hikurangi Plateau (New Zealand) from seismic reflection imaging (2024)

Seismic evidence of magmatic rifting in the offshore Taupo Volcanic Zone (2019)

A >400 km long seismic reflection profile showing five large seamounts on the Hikurangi Plateau large igneous province from Gase et al, 2024 - in Geosphere.

~1000 earthquakes from a year-long ocean-bottom seismometer array offshore Southeast Alaska

Transform faults

Most earthquakes occur on tectonic plate boundaries beneath the oceans, far from seismic monitoring networks. Many of these faults still pose hazards to society and rare studies of their seismicity show that they can have diverse modes of slip. We are working with U.S. and Canadian scientists to characterize seismicity on Southeast Alaska's Queen Charlotte Fault with a network of ocean bottom seismometers.

You can view preliminary work in this poster

Ocean bottom seismometers on the deck of the R/V Langseth. Image courtesy of L. Worthington.

Multi-offset 100 MHz ground-penetrating radar acquisition at Mount St Helens

Near-surface geophysics

With ground-penetrating radar and seismology, we can predict water content and rock properties, and map stratigraphy within the Earth's upper ~50 meters. These methods are widely used in geotechnical and hydrological surveys and can be adapted to study many natural processes. In this example, we used ground-penetrating radar to map pyroclastic flow units from the May 18 1980 Plinian eruption of Mount St Helens. Electromagnetic and seismic velocities can jointly analyzed to estimate subsurface water-content and porosity.

Select publications:

Estimation of porosity and water saturation in pyroclastic deposits (2018)

Evidence of erosional self-channelization of pyroclastic flows from GPR (2017)

50 MHz radar image and a nearby outcrop for comparison, at Mount St Helens pumice plain, from Gase et al. 2017 - in Geophysical Research Letters.

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