Hi All. It looks like Spokane is getting jousted again so I thought I would take a look see as to what could be found in the way of past history for quakes in the area of Spokane. About the only thing I could find was that there some events felt only in and around Spokane occurred in 1915, 1920, 1922, 1941, 1942, 1948, 1952, 1961 and 1962. In some instances the shaking was accompanied by explosion-like noises, and in some cases several events close together in time were reported. No extended sequence like the current activity is known. At this time I really haven't found anything much beyond that and what is already known concerning the most recent activity in and near Spokane.

On July 30, at 6:38PM PDT a magnitude 3.2 earthquake occurred near Spokane. This had been the largest event since June 25 until November 11 when a magnitude 4.0 earthquake occurred at 8:00AM PST. On November 11, the magnitude 4.0 earthquake was followed by a magnitude 3.1 earthquake at 9:21AM PST a 3.1 at 7:02PM PST a magnitude 3.3 earthquake at 7:03PM PST a 1.9 earthquake at 9:07PM PST and a 2.4 earthquake at 9:11PM PST.

It is a bit difficult to pinpoint exactly when the sequence commenced, as Spokane is at the edge of the PNSN, and the nearest stations, NEW and DPW are more than 60 km away from the activity. The sequence included a possible foreshock, magnitude 2.0, on May 24. It is not clear whether the May 24 event was felt.

On June 25, the largest earthquake in the sequence to date occurred. It was felt by hundreds of people throughout Spokane, and located beneath downtown Spokane near Gonzaga University. Magnitude estimates were 3.9 (Mc) and 3.7 Ml using local magnitude. The June 25 mainshock caused some minor damage as bricks tumbled from a few chimneys, and a few dishes fell from shelves, etc. By the end of June, The PNSN had located 21 earthquakes (11 reported felt) within about 11 km of Gonzaga University.

Reports of unrecorded felt earthquakes (nearest data collectors were about 60Km distant at the time) continued despite the new station, and the PNSN continued to record aftershocks of magnitude 2.0 and larger through June. In addition to the recorded earthquakes, residents of certain neighborhoods in Spokane continued to report feeling shaking at times when the instruments recorded nothing. Most of these shaking reports were confined to a limited geographic area in the part of the Spokane immediately north of downtown. Reports of explosion-like sounds accompanying the shocks are common.

These features of the Spokane quakes (noise, not being recorded by PNSN instruments, and being felt over tiny areas) mean that they are probably extremely shallow and very close to the areas where they are being felt and heard.

Although never previously noted near Spokane, earthquake swarm activity; defined as a cluster of small close-together earthquakes without a very sizable mainshock; has previously been seen in eastern Washington. One notable swarm occurred near Othello and lasted nearly a year. It began in November of 1987 and included about 200 located earthquakes, about 20 of them larger than magnitude 2.0. The largest event in the Othello sequence was magnitude 3.3.

None of the past damaging earthquakes in Washington or Oregon was preceded by any noticeable foreshock activity. There always the first time for everything.

Mike Zientek of the USGS Spokane Office has stated that geologists have long suspected that the course of the Spokane River was structurally controlled. It flows east to west toward Spokane, where it abruptly changes to a northwest direction. Hangman Creek (also called Latah Creek) flows into the Spokane River near the bend along the same NW striking lineament. This lineament is clearly expressed in the topography, particularly along Hangman Creek, which is quite straight compared to the complex dendritic pattern more commonly displayed by other drainage in this area. Bob Durkey of the Washington State Dept. of Natural Resources has mapped the Hangman Creek watershed, and named this structure the Latah Creek Fault.

However, direct evidence for faulting is skimpy:

At Hangman Valley Golf course flood deposits are uptilted to 35 degrees.
Well data from either side of Hangman Creek shows elevation or thickness differences in the Grande Ronde CRB flow. However, the flow was deposited onto a Miocene landscape and it is difficult to determine whether differences result from flows interacting with the ancient landscape or from faulting.
Likewise exposures of basalt along the near "Bowl and Pitcher" in Riverside State Park differ from what is seen at "Five Mile Prarie" across the river. However it is also difficult to pinpoint the cause of this.

As it can be seen there is quite a bit that is known, but not really understood. Ah, such is life. If only we understood everything we know, or think we know. Nature surrenders her secrets only when she's ready, or does she? Take Care…Don in creepy town