Caldera Records: How the 1959 Lake Hibgen Earthquake May Continue to Influence Earthquakes in Yellowstone Today | national news

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators at the Yellowstone Volcano Observatory. This week’s contribution is from Mike Stickney, director of the Office of Seismic Studies at the Montana Bureau of Mines and Geology.

Greater Yellowstone has undergone significant deformation. Within the Yellowstone Caldera, average elevation rates as measured by settlement, GPS, and Insar generally range from 10 to 30 mm per year. While rates of elevation measured in mm/year may seem small, if this elevation persisted through geologic time – say a million years – the Earth’s elevated surface would be more than 10 kilometers (6.2 mi) – much higher than Mount Everest.

It is clear that this rise cannot continue for long periods of time. In fact, deformation measurements indicate an equally large subsidence of the caldera during historical times – the Earth is moving up and down. Prehistoric shores around Yellowstone Lake testify to the rise and fall of the caldera over the past millennia, with cumulative movement moving downward by tens of meters (yards). Researchers attribute this rise and fall of the Earth’s surface to the accumulation and discharge of fluids – magma, gas and water – below the surface.

Studies have also documented rapid deformation outside the Yellowstone Caldera, particularly in the Hepgen Lake region. During 1973–1987, a trigonal scan, which measures horizontal deformation, revealed 8 mm/yr of NNE-SSW-guided stretching or stretching. The measured extension rate was constant over 14 years of measurements and was concentrated in an area roughly coinciding with the central region of the 1959 Lake Hepgen earthquake.

The authors of the article reporting the triangulation results suggested that the deformation was related to the extension of the magmatic system in the Yellowstone Caldera, since the deformation zone was associated with earthquakes that headed at least 100 km from the erupting Tyre Creek dome in the northeast. Part of the caldera west to south of the Madison Valley.

But does such a molten system really exist? No other lines of evidence seem to support this hypothesis. For example, there are no recent volcanic eruption centers or thermal springs west of the Yellowstone National Park boundary in the Hepgen Lake region. The area is seismically active, but earthquake swarms that characterize much of the seismic activity within the park are not uncommon west of Hebegin Lake.

This graphic shows the foci of 6,188 earthquakes in the Hibgen Lake region since 1990, identified by seismological stations at the University of Utah and the Montana Bureau of Mines and Geology.

Smith

Rather than intrusion of magma, could the deformation in the Heipgen Lake region be related to the effects of the 1959 earthquake?

One intriguing piece of evidence is the relationship between persistent seismic activity and the deformation that accompanied the 1959 earthquake. After this event—one of the two largest ever recorded in Intermountain West in the United States (the other occurred in Nevada in 1915)—geologists at the Geological Survey used The U.S. surveyed flat along Highway 287 (which runs along the northern shore of Lake Heipgin) and crooked beaches along Lakes Heipgin, Cliff, and Wade to create a earthquake deformation map. The map shows a dramatic subsidence (up to 21 ft) in the northwest portion of Heipgen Lake, with the subsidence declining southward away from two primary faults (Heibgen and Red Valley) that ruptured in 1959.

An overlay of a map of precisely located seismic foci on the deformation shows that the vast majority of earthquakes have been located west of Yellowstone Park since 1990, when the Yellowstone and Montana seismic networks together began to provide excellent coverage of this region, falling within the 1959 subsidence zone. The seismic zone extends eastward into Yellowstone National Park, and an earthquake-related subsidence has been observed near the Norris Geyser Basin, so it is possible that the most recent earthquake zone corresponds to the 1959 subsidence zone between Lake Hepgen and the Norris Geyser Basin—the most seismically active area of ​​Yellowstone Park. the National.

This house fell into Heipgen Lake during the 1959 earthquake and floated along the shore until it settled here. The homeowner, 70-year-old Mrs. Grace Miller, only escaped after being kicked out of her front door and jumping into a 5-foot-wide crack when her home plunged into the lake.

Hadley, JB

The most intense west of Yellowstone earthquake extends about 10 kilometers west of the park boundary to the eastern edge of the main body of Lake Heipgen, which is also roughly the meridian of the 1959 earthquake’s epicenter and the eastern end of the Hepgen fault. Minor earthquakes feature the main body of Hepgen Lake and are adjacent to the Southern Madison Mountain Range to the west.

The area between the Madison Fault and the Cliff and Wade Lakes is another recent earthquake hotspot. Most of these earthquakes are located in the southern Madison Valley within the circumference of a one-foot subsidence of the 1959 deformation, but a distinct group of earthquakes extends north into the Madison Range, mostly to the east of the Madison Fault plunging to the west. Finally, west of Lakes Cliff and Wade, the earthquakes continue westward for more than 350 kilometers along a direction extending across southwestern Montana into central Idaho.

The relationship between the most recent earthquake hotspots in the Lake Heipgen region and the subsidence zone of the 1959 earthquake suggests that these earthquakes may represent the aftershocks of the 1959 Lake Heipgen earthquake. A growing body of evidence from other historical earthquakes indicates that mega-seismic events that occur on low-slip rate faults with Long repetition periods may have backsliding sequences lasting for many decades or even centuries. The deformation measured during 1973-1987 may also be related to the earthquake. If future surveys show that the rate of extension slowly decreases over time, that suggests that post-earthquake deformation could persist for decades to centuries, much like aftershock sequences.

Continuous monitoring of the Hepgen Lake Basin/South Madison Valley with improved seismic instruments and GPS will provide critical data to determine whether we are still seeing aftershocks and expansion from a major earthquake there more than six decades ago, and will help to better understand these Continuous seismic zone in the Yellowstone region.

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