Magmatic system structure and seismicity of the Three Sisters volcanic complex

This project investigates the Three Sisters volcanic complex in central Oregon. It will use seismic observations and methods to advance understanding of volcanic hazards and the fundamental processes that create different types of volcanoes and magma types. This volcanic system is active, and the presence of nearby population centers means the Three Sisters is classified as a Very High Threat volcanic system for the U.S.

The Three Sisters volcanic complex includes a wide variety of volcanic structures and geologically young lavas (about 2,000-years old). Additionally, about two decades of satellite data show that areas near the volcanoes are deforming due to inflation under the surface. Existing data are scarce partly because the immediate vicinity of the volcanoes is a difficult to access and federally protected Wilderness.

This project will add observations in these areas by using small temporary seismic instruments, that can be transported on foot and do not require digging, to address both the accessibility challenges and the need for minimal impact. Combining the new temporary seismic data with modern imaging and earthquake detection methods, the researchers will gain a systematic view of subsurface structures.

This will assist in more rigorously understanding the record of prior eruptions and ongoing monitoring of deformation. The seismic data collection and analysis will engage students from multiple institutions and personnel from regional hazard monitoring agencies to promote professional training and communication to stakeholders.

The Three Sisters volcanic complex is classified by a U.S. Geologic Survey report as a Very High Threat system, with geodetic evidence for ongoing surface deformation, lava flows as young as about 1,600-years, and Holocene eruptions of compositions ranging from basaltic andesite to rhyolite. Yet, there is little knowledge of the 3-D distribution of middle to upper crustal magma storage and microseismicity beneath this multi-vent volcanic complex located within the High Cascades graben.

Observational seismology has been limited by the need for minimal impact in a large federal Wilderness. The project will deploy an array of low-impact nodal seismometers to provide the first local imaging of the Three Sisters magmatic system. Analysis of the data will advance understanding of how magma reservoir structure in multi-vent systems is linked to spatial variations in edifice construction and erupted compositions, with dominantly basaltic andesite in the northern part of the volcanic complex transitioning to more prevalent rhyolite eruptions at the southern end.

Seismic imaging with the new temporary network data will begin with relatively conventional ambient noise surface wave tomography and then push the boundaries of temporary nodal array imaging by applying anisotropic adjoint tomography. The influences of edifice topography and radial anisotropy on magma reservoir imaging will be tested with numerical 3-D wave propagation and inversion methods.

The new data will also be used to scrutinize microseismic activity and conduct receiver function imaging of localized interfaces, which could better define interactions between tectonic and magmatic deformation structures.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.