Presentation Type

Poster Presentation

Category

STEM (science, technology, engineering, mathematics)

Abstract/Artist Statement

Western Montana is home to a significant amount of continuous, complex seismic activity due to the fact that the region lies within the Intermountain Seismic Belt (ISB). The ISB is a 100 km wide seismic belt that stretches along western Montana, reaching from Yellowstone National Park to northwest Montana, and is responsible for much of the state’s seismic activity. Like many seismically active areas, Western Montana’s earthquakes are best studied through the use of seismographs. Data from these instruments can be used to create crustal velocity models for an area within the seismic network. Velocity models are powerful tools that effectively describe seismic velocity as a function of depth and are used to enhance our understanding of an area’s crustal structure, crustal stress conditions, and earthquake hypocenter locations. In areas that are seismically active, it’s important that these models are updated regularly. However, the velocity model currently in use for Western Montana was last updated in 2003. This is because, even though Montana experiences numerous earthquakes every year, many of these earthquakes are low in magnitude, averaging from M 1.0 - M 3.5. These low magnitude earthquakes do not typically produce enough data to create or update velocity models. Oftentimes, we require much larger events (≥ M 5.0), ideally with a strong aftershock sequence. Historically, for western Montana, such events are intermittent and sometimes decades apart. We will derive a new 1-D crustal velocity model for west-central Montana by analyzing seismic-phase arrivals from the M 5.8, 6 July 2017 earthquake that occurred 11 km southeast of Lincoln, Montana, and hundreds of aftershocks that followed over a three-year period (2017-2020). The 2017 Lincoln earthquake was the largest event above M 5.5 to occur in western Montana in over half a century, the last being the 1959 M 7.3 Hebgen Lake earthquake in southwestern Montana. To determine the velocity model, we manually retrieve continuous seismic data recorded by broadband stations in the University of Montana Seismic Network, which have been strategically deployed to study the Lincoln aftershock sequence, supplemented by telemetered data from the Montana Regional Seismic Network. To constrain the model, we invert phase arrivals from several hundred well-recorded earthquakes (>20 phase arrivals) using the software program VELEST. The final model will characterize the crustal velocity structure appropriate to an area in western Montana of about 5000 km2. Due to western Montana’s proclivity towards infrequent, high-magnitude earthquakes, the 2017 Lincoln event has provided a prime opportunity to collect quality seismic data that will allow us to create a much-needed crustal velocity model for this seismically active region of Montana. Not only will developing a new, regional crustal velocity model advance earthquake science in Montana, but this will also be the first model derived specifically for the west-central region of the state, as the current velocity model is most appropriate for southwestern Montana. With our model, we will be able to provide the first accurate crustal velocity structure and method to locate hypocenters for the west-central region.

Mentor Name

Hilary Martens

Personal Statement

This project is significant to me for a few reasons. First and foremost, this event is the largest magnitude earthquake above M 5.5 to occur in the state of Montana since 1959; over half a century. Not only that, but this earthquake has been followed by a prolific aftershock sequence that is still ongoing today. Given the state’s intermittent seismic activity, it can prove difficult to effectively study and understand the region’s seismology. Therefore, the Lincoln earthquake has given us a prime opportunity to create a crustal velocity model for west-central Montana, something that has never been done before! The last crustal velocity model derived for western Montana was determined seventeen years ago in 2003. While influential, this model has become antiquated. We are in need of not only a revised model, but a functional process to derive this model and future models. Before the 2003 model, only two previous models existed, which were derived in 1997 and 1984. The downfall of these models is the lack of high quality seismic data used to create them. Aside from the fact that the last major earthquake occurred in 1959, the seismic stations used to collect data for the models were composed of short period, analog, one-component seismometers, which provided limited details on recorded earthquakes. For our model, seismic data will be collected via digital, broadband, three component seismometers. This is a significant upgrade in technology that yields highly detailed seismic data. We anticipate this upgrade in technology will lead us to develop a crustal velocity model that can be used to locate hypocenters and determine crustal structure with notably greater accuracy. Once we determine an appropriate, efficient process to utilize seismic data to create a 1D model for our study region, this process can be used for other seismically active regions of western Montana. With models created for various regions of western Montana, we can treat these individual models as ‘puzzle pieces’ and, together, form a single, cohesive model for the western portion of the state. This would undoubtedly advance earthquake science in Montana. Finally, this project is of great importance to me as my professional goal is to have a career of researching volcanic eruptions and the movement of magma below the surface. These topics involve a great deal of seismology, which is the focus of my M.S research. This project will provide the experience and skills I need to further my knowledge of creating seismic velocity models as I am certain it will prove invaluable as I work towards my Ph.D. and give me a solid foundation to build upon as I start my career.

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1D Crustal Velocity Model for West-Central Montana

Western Montana is home to a significant amount of continuous, complex seismic activity due to the fact that the region lies within the Intermountain Seismic Belt (ISB). The ISB is a 100 km wide seismic belt that stretches along western Montana, reaching from Yellowstone National Park to northwest Montana, and is responsible for much of the state’s seismic activity. Like many seismically active areas, Western Montana’s earthquakes are best studied through the use of seismographs. Data from these instruments can be used to create crustal velocity models for an area within the seismic network. Velocity models are powerful tools that effectively describe seismic velocity as a function of depth and are used to enhance our understanding of an area’s crustal structure, crustal stress conditions, and earthquake hypocenter locations. In areas that are seismically active, it’s important that these models are updated regularly. However, the velocity model currently in use for Western Montana was last updated in 2003. This is because, even though Montana experiences numerous earthquakes every year, many of these earthquakes are low in magnitude, averaging from M 1.0 - M 3.5. These low magnitude earthquakes do not typically produce enough data to create or update velocity models. Oftentimes, we require much larger events (≥ M 5.0), ideally with a strong aftershock sequence. Historically, for western Montana, such events are intermittent and sometimes decades apart. We will derive a new 1-D crustal velocity model for west-central Montana by analyzing seismic-phase arrivals from the M 5.8, 6 July 2017 earthquake that occurred 11 km southeast of Lincoln, Montana, and hundreds of aftershocks that followed over a three-year period (2017-2020). The 2017 Lincoln earthquake was the largest event above M 5.5 to occur in western Montana in over half a century, the last being the 1959 M 7.3 Hebgen Lake earthquake in southwestern Montana. To determine the velocity model, we manually retrieve continuous seismic data recorded by broadband stations in the University of Montana Seismic Network, which have been strategically deployed to study the Lincoln aftershock sequence, supplemented by telemetered data from the Montana Regional Seismic Network. To constrain the model, we invert phase arrivals from several hundred well-recorded earthquakes (>20 phase arrivals) using the software program VELEST. The final model will characterize the crustal velocity structure appropriate to an area in western Montana of about 5000 km2. Due to western Montana’s proclivity towards infrequent, high-magnitude earthquakes, the 2017 Lincoln event has provided a prime opportunity to collect quality seismic data that will allow us to create a much-needed crustal velocity model for this seismically active region of Montana. Not only will developing a new, regional crustal velocity model advance earthquake science in Montana, but this will also be the first model derived specifically for the west-central region of the state, as the current velocity model is most appropriate for southwestern Montana. With our model, we will be able to provide the first accurate crustal velocity structure and method to locate hypocenters for the west-central region.