Texas Panhandle residents got a reminder from nature this past weekend that it takes force and motion to shape the region's hills, mesas, and picturesque vistas.
A 4.0-magnitude earthquake centered about nine miles north-northeast of downtown Amarillo jolted the countryside at 8:04 a.m. Saturday (Oct. 20). There weren't any reports of injuries or damage but social media erupted soon after with reports of low rumbles, vibrating walls, rocking beds and couches, and startled pets.
As with all earthquakes, people can engage in citizen science. The U.S. Geological Survey is collecting as many reports as it can obtain of what people felt through its "Did You Feel It?" feature. (Click "Felt Report - Tell Us!" on this page.)
The USGS' Earthquake Hazards Program then uses the data to compile a map of the earthquake's effects, along with other interesting data the agency provides about the earthquake.
As of Monday, several hundred responses had been filed from 76 ZIP codes across the Panhandle, ranging from people saying they didn't feel anything to those who said they definitely did. Some responses are from people so far away that almost certainly must be false reports (Alabama and Minnesota, for example).
Here's the map as of noon Monday:
History and intensity
Though infrequent, earthquakes are not rare in the Texas Panhandle.
Geologically, the area north of Amarillo where Saturday's quake was centered, has known faults that are tied to what geologists call the Amarillo-Wichita Uplift. Think of it as a chain of underground mountains trending from east to west that began forming about 600 million years ago when the Earth's crust began to pull apart and form a rift zone in the region. That rifting, however, stopped, leaving the ridges and associated faults behind.
The largest known quake in Texas Panhandle history struck on July 30, 1925. A series of small shocks led up to a larger shock that was centered near Panhandle. Those were the days before the Richter scale had been invented, but the effects of the largest quake that day were similar to roughly a magnitude 5.4, records show. That quake was followed one day later by a 3.0-magnitude tremor in White Deer.
Other notable Texas Panhandle quakes larger than Saturday's tremor include an approximate 5.0-magnitude quake centered near Borger on June 19, 1936; and a 5.2-magnitude quake that shook Dalhart and surrounding areas on March 11, 1948.
Saturday's quake so far has an assigned intensity of IV on the Modified Mercalli Intensity (MMI) Scale, which is another way to measure strength of shaking.
MMI level IV is characterized as "light" shaking:
- "Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably." (Source: USGS)
For comparison, the quakes of 1925, 1936, and 1948 mentioned above all had estimated MMI intensities of VI, or strong enough to be felt by everyone and powerful enough to move heavy furniture and cause cosmetic damage to buildings.