Observational and Experimental Seismology
Dr. Keith Koper's Research Group at the University of Utah
Discrimination of Earthquakes and Explosions at Local Distances
The field of verification seismology uses seismic observations to detect, locate, and characterize nuclear explosions. A major challenge in this field is distinguishing nuclear explosions from more commonly observed earthquakes. Seismologists are very successful at doing this for moderate seismic events (M3–5) recorded at regional distances (200–2,000 km). A current challenge is extending these methods to work for small seismic events (M0–2) recorded at local distances (<200 km). With funding from the Air Force Research Laboratory (AFRL), we are exploring new methods of distinguishing small chemical explosions from small earthquakes in the Utah region. The chemical explosions are related to military and industrial activities, and serve as surrogates for nuclear explosions in our analysis.
Imaging the Fine-scale Structure of Earth's Inner Core
Earth's inner core is solid iron-nickel alloy that resides at the center of the Earth. It has a radius of 1221 km, which is about the same size as the dwarf planet Pluto. The inner core is slowly growing as the Earth cools and the liquid outer core freezes. The inner core has an unexpectedly large amount of fine-scale heterogeneity. It is unclear whether this heterogeneity is related to pockets of partial melt, variations in chemical composition, or misalignment of iron grains. With funding from the National Science Foundation (NSF) we are currently using very tiny seismic reflections from the inner core to map out its interior structure.
Characterization of Mining Induced Seismicity in Utah
Utah has a long history of underground coal mining. The removal of coal creates small seismic events that are commonly recorded by our regional seismograph network. These events are referred to as mining induced seismicity. We work to better understand the mechanism of these events (e.g., collapses vs. shear dislocations), to determine high-precision relative locations, and to determine magnitude-time histories. Our work is funded by the National Institute for Occupational Safety and Health (NIOSH) and is done in collaboration with colleagues from the Department of Mining Engineering. Our results help mines improve the safety of their operations.
Analysis of the 2020 Magna, Utah, Earthquake Sequence
On 18 March 2020 an Mw 5.7 earthquake occurred in Magna, Utah near Salt Lake City. It occurred on the Salt Lake City Segment of the Wasatch Fault Zone, a large normal fault system in Utah. This is the largest earthquake to occur in Utah since 1934, is the largest earthquake on the Wasatch Fault Zone recorded by seismometers, and is the largest earthquake most residents of northern Utah have felt. The mainshock was recorded by ~120 permanent seismograph stations within 150 km. Following the mainshock, 180 three-component, Fairfield Nodal seismometers were deployed around the Salt Lake Valley for one month. Between 18 March 2020 and 30 April 2020, 2,102 aftershocks were located by the University of Utah Seismograph Stations. Concluded and ongoing analysis of this sequence includes detection of events using machine learning, moment tensor inversion, spectral modeling of the mainshock, template-based detections of aftershocks, b-value estimation, and high-precision relocation of aftershocks. These analyses have created a better image of the Salt Lake City Segment of the Wasatch Fault and understanding of potential seismic hazards.
Discovering Hidden Earthquakes in Yellowstone
~2000 earthquakes are detected by the University of Utah Seismograph Stations in the Yellowstone region every year. However, it is likely that many small earthquakes are not being detected using traditional methods because their signal is often masked by the noise also recorded on seismometers. We use machine learning and template matching techniques to find these earthquakes and create a robust catalog of important information such as phase arrival times, first motions, and locations. The enhanced catalog of seismic events in the Yellowstone region will allow for the unprecedented high-resolution imagining of magma beneath the calderas, detailed analysis of fault architecture, mapping of swarm kinematics relating to fluid transport, and analysis of dynamic triggering of local earthquakes by large surface waves passing through.
Analysis of Microseisms from Yellowstone Lake
Microseisms are vibrations in the Earth created by oceans waves. Unlike transient signals from earthquakes, they are observed almost continuously, even at stations far away from coastlines. Recently, we discovered that waves from lakes also create microseisms. With funding from the National Science Foundation (NSF), we are currently deploying portable seismometers around the shore and along the bottom of Yellowstone Lake to better understand how this energy is created and whether it can be used to make high-resolution images of the subsurface in Yellowstone National Park.
Analysis of the 2019 Bluffdale, Utah, Earthquake Sequence
A sequence of 191 earthquakes occurred near Bluffdale, Utah, between 13 February 2019 and 15 April 2019. The largest event occurred on February 15th with a magnitude of 3.7 MW and was felt by nearly 9,000 residents of the greater Salt Lake City area. With funding from the State of Utah, we are currently utilizing waveform correlation and a similarity-based relocation algorithm to analyze the sequence of events. We are also using template-matching methods to detect and locate other earthquakes in the sequence that were too small to be detected with conventional processing. Our goals for this research are to investigate the possible relationship of this sequence to the Wasatch Fault, analyze the complex nature of the tectonic setting surrounding the Bluffdale region, and improve our understanding of earthquake hazards in this densely populated area.
Analysis of the 2019 Clawson, Utah, Earthquake Sequence
A sequence of over 180 earthquakes occurred near Clawson, Utah, between 13 March 2019 and 27 May 2019. The largest event occurred on April 10th, with a magnitude of 3.2 ML. This sequence was lightly felt because of its location in the relatively remote San Rafael Swell region. With funding from the State of Utah, we are currently measuring high-resolution differential travel times and relocating this sequence of events. We are also using template methods to detect and locate other earthquakes in the sequence that were too small to be detected with conventional processing. We are trying to determine the number and orientations of the faults involved in this sequence, and their relationship to the M5.2 earthquake that occurred in the San Rafael Swell in 1988.
