YELLOWSTONE NATURE NOTES

EARTHQUAKE HISTORY OF IMMEDIATE AREA

F. V. Hayden, leader of the first scientific exploration party of the Yellowstone area, reported (1872, p. 82),

"While we were encamped on the northeast side of the lake, near Steamboat Point, on the night of the 20th of July (1871), we experienced several severe shocks of an earthquake, and these were felt by two other parties, fifteen or twenty-five miles distant, on different sides of the lake. We were informed by mountain men that these earthquake shocks are not uncommon, and at some seasons of the year very severe, and this fact is given by the Indians as the reason why they seldom or never visit that portion of the country. I have no doubt that if this part of the country should ever be settled and careful observations made, it will be found that earthquake shocks are of very common occurrence."

A. C. Peale, mineralogist and member of the Hayden expedition has recorded the following in the same volume, (p. 189-190):

"On the 19th of August we moved our camp down the Lake to Steamy Point . . . Our camp was situated on a high bluff on the edge of the lake . . . Every night while at this place we experienced earthquake shocks, each lasting from five to twenty seconds. We named it Earthquake Camp."

This earliest record of seismic activity in the park was also noted by Captain J. W. Barlow, leader of a second scientific expedition encamped on the southeast arm of Yellowstone Lake. Barlow's report (1872, p. 38-39) contains the following entries:

August 20, 1871—"We experienced last night the singular sensation of an earthquake. There were two shocks, the first one being quite severe accompanied by a rumbling and rushing sound."

On the 21st of August, Barlow had joined the Hayden camp at Steamboat Point and notes once again (op. cit., p. 39),

". . . frequent earthquake shocks were felt by the party while at this camp."

Apparently the tremors had been impressive enough to cause Barlow to comment once again on the 22nd of August, (op. cit., p. 39) where he was encamped near the Lower Falls of Yellowstone River,

"During the night the concussion caused by the falling water reminded me of the earthquakes felt on the lakes a few nights previous."

In the years since the Hayden Survey the adjoining states have been subjected to many earthquakes.

TABLE 1. Stronger Earthquakes in Surrounding Area

It seems that on an average of about once every ten years a strong earthquake is registered in the adjoining states.

Yellowstone has had its share of tremors. Table 2 presents a summary of available data but should not be considered as all inclusive because of a number of factors: Reporting of earthquakes was done haphazardly for many years and much of the park is primitive wilderness area untouched by man and seen only rarely during the summer months. With the approach of winter the park is gradually closed and only a few outpost stations are manned throughout the year. Many tremors must have passed un-noticed in this great wilderness area. To quote the words of Dr. Stephen W. Nile, Collaborator in Seismology for the U.S. Coast Geodetic Survey at Butte, Montana, "If only the Moose and Elk could talk!"

The frequency, intensity, and epicenters* of known earthquakes in the Yellowstone area have been recorded on Plate 36 (back of book) and in Table 2. Certain inferences seem apparent. The South Entrance, Yellowstone Lake, Old Faithful, and Mammoth appear to have been the most active areas prior to 1959.

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*Note. The accuracy of epicenter determinations is dependent upon the number and quality of the seismograms. For example, an epicenter determined at 45-1/2° N. Lat. is less accurate than one determined at 45° 30' but both are plotted on the map in the same place.

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The 1959 main shock and aftershocks have centered largely in the northwestern corner of the park around the Gallatin Mountain Range. The one most active aftershock epicenter has been at 45° N. Latitude and 111° W. Longitude.

TABLE 2. Seismic History of Yellowstone National Park

References

(1) Hayden, F. V., et al., 1872, Fifth Annual Report of the U.S. Geological and Geographical Survey of the Territories for 1871, p. 82.

(2) Barlow. Captain J. W., and Heap, Captain D. P., 1872, Report of a reconnaissance of the basin of the upper Yellowstone in 1871, p. 38.

(3) Newspaper reports from local area on file in Yellowstone Park Library.

(4) U.S. Coast and Geodetic Survey, United States Earthquakes, Dept. of Commerce Publications.

(5) Superintendent of Yellowstone National Park Annual Report for 1915, p. 27.

(6) Seismograph Station records at Montana School of Mines, Butte, Montana.

(7) Monthly Report of U.S. N.P.S. Ranger Nat. Lacy for Shoshone Lake, 1955.

(8) Correspondence from David O. Bittner, Mt. Holmes Fire.

Before attempting to explain why earthquakes occur here it would be best to examine the position of the park in terms of the seismic pattern of the United States. Figure 1 plots the distribution of earthquakes in the United States through 1957. Of particular interest is the belt of earthquakes that follows the Rocky Mountain zone of overthrust faults in Montana and then shifts westward in Utah to follow the Wasatch Mountain front southward into Arizona. This is a major zone of weakness in the earth's crust that has been responding to the accumulation of stresses throughout recorded human history.

Watching the shifting pattern of epicenters during 1959 (Plate 36) seems suggestive of block faulting, with a shift on one block putting a neighboring block out of gravitative balance. Continued adjustments have taken place with several thousand aftershocks being recorded in the months following the initial displacement.