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Regional Earthquake Recordings

This example illustrates waveforms from a moderate regional earthquake using an event in Utah.

A magnitude 5.9 event, this earthquake produced a maximum of intensity VI. Reports to the NEIC include some damage (VI) at Cedar City, Hurricane, Kanab, New Harmony, Santa Clara, Springdale, St. George, Toquerville, Virgin, and Washington. The earthquake triggered a large landslide which destroyed three houses at Springdale. At other intensities, the event was felt (V) at Glendale, Gunlock, Hatch, Kanarraville, La Verkin, Orderville, Panguitch, and Rockville; (IV) at Alton, Beaver, Beryl, Brian Head, Bryce, Circleville, Enterprise, Escalante, Junction, Milford, Minersville, Modena, Mt. Carmel, Newcastle, Parowan, Richfield, and Tropic.

The event was felt throughout much of southwestern Utah, northwestern Arizona, and southeastern Nevada as far south as Flagstaff, Arizona and as far north as Richfield, Utah. Felt west as far as Caliente and Pioche, Nevada and southwest to the Las Vegas, Nevada area.

Information from the USGS NEIC
Location: Utah
Date: 92/09/02
Origin Time (UTC): 10:26:20.9
Location: 37.090, -113.472
Depth (km): 15.0
Magnitude: 5.9 ML

A map illustrates the location of this earthquake in the Western United States. The circle denotes the location of the epicenter and the squares indicate the sites of several BDSN seismometers. The solid lines indicate the location of major active faults.

This event was well-recorded by all stations of the BDSN. This figure compares recordings from 4 sites on the same plot. These seismograms are plotted with amplitude as a function of time. These are raw waveforms and represent the recorded ground velocity on the vertical component sampled at 20 Hz (the BHZ channel). The traces are ordered by distance, with the closest station (CMB) at the bottom and the most distant station (ARC) at the top. The traces are plotted with absolute amplitude. At these distances, the waveforms vary more slowly with distance and no single trace dominates the plot (as compared to the local example. For each station, the distance to the earthquake in degrees is labeled above the trace at the right edge of of the plot, while the maximum amplitude is labeled below.

For comparison, this figure shows the same seismograms, plotted to illustrate the variation with distance. This "record section" shows the traces at their true distance between 5 and 10 degrees. Below are three separate record sections are plotted for the three components of motion. In this case, the horizontal components have been rotated from North and East into a reference frame parallel and perpendicular to the great circle containing the earthquake and the station. In this reference frame, the "radial" component (labelled BHR) display motion in the plane between the earthquake and the station and the "transverse" component (labelled BHT) display motion perpendicular to that plane. The traces have been filtered to accentuate the low-frequency arrivals.

Seismogram of a regional earthquake recorded on the vertical component. Seismogram of a regional earthquake recorded on the radial component. Seismogram of a regional earthquake recorded on the tangential component.

The examples below include plots of the three components of ground motion (BHZ - Vertical, BHN - North, BHE - East) recorded at 4 stations. Each plot show amplitude as a function of time, with 9 minutes of record displayed in each figure. The "absolute" time of the plot is marked on the lower left.

Waveforms from the BDSN
CMB
  • Distance = 619.64 km
  • Azimuth = 281.83 degrees

Three traces of seismogram wiggles, one for each direction, recorded at atation CMB
SAO
  • Distance = 711.13 km
  • Azimuth = 269.49 degrees

Three traces of seismogram wiggles, one for each direction, recorded at atation SAO
BKS
  • Distance = 779.75 km
  • Azimuth = 279.08 degrees

Three traces of seismogram wiggles, one for each direction, recorded at atation BKS
ARC
  • Distance = 1009.62 km
  • Azimuth = 297.85 degrees

Three traces of seismogram wiggles, one for each direction, recorded at atation ARC