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Geometrics' Seismograph Records Alaskan Earthquake

Jul 21, 2017 | Posted in Blog, News

On July 17, 2017 at approximately 4:30 pm San Jose, California time, a magnitude 7.7 earthquake struck the far western tip of the Aleutian Islands, near Nikol'skoye, Russia. The USGS estimates that the quake resulted from movement along a right-lateral transform fault on or near the Pacific and North American plate boundaries. Later analysis indicates that the focal point for this earthquake is approximately 11 km deep with a rupture plane on the order of 170 km long by approximately 20 km wide (as viewed in cross section).

Figure 1

Figure 1 – Location of July 17, 2017 earthquake and distance from the Geometrics’ Office in San Jose, California.

At Geometrics in San Jose, approximately 5,300 kilometers away from the epicenter, Dr. Koichi Hayashi of OYO Corporation had a Geometrics Atom Wireless system with a 3-component 2 Hz geophone sitting on the floor of his office. The Atom was recording local ambient ground motion when it received the P, S, and surface waves from the earthquake. By the time ground motion from this quake reached San Jose, it was so weak that it was not noticeable except to the most sensitive instruments.

Figure 2

Figure 2 – Picture showing a 2-Hz triaxial geophone sitting on a brick on the floor of Dr. Hayashi’s office. The three Geometrics’ Atom Seismographs are shown in the back, each recording a different axis.

After processing the data, Dr. Hayashi observed a large earthquake signal and identified the event on the USGS Earthquake Hazards page. The Atom Seismograph sitting on the floor of a commercial building is so sensitive that it clearly picked up ground motions in the X, Y, and Z directions for an earthquake thousands of kilometers away. We should also note that the Geometrics’ offices are located between two major freeway systems (Highways 680 and 880) in the heart of Silicon Valley and that the earthquake occurred during rush-hour when both freeways and many surface streets have high traffic counts. This extraneous noise can have a significant effect on the ability to detect earthquake data.

Figure 3

Figure 3 - Raw data collected from the Atom on the floor with the 2-Hz triaxial geophone.

Figure 4

Figure 4 - This figure shows the same data as in figure 3, except that Dr. Hayashi used a low-pass filter with a period of 1 second. The earthquake is clearly visible once the high-frequency noise is attenuated.

Figure 5

Figure 5 - This figure shows the same data as in figure 3, except now the low-pass filter has a period of 10 seconds (0.1 Hz). At this level the surface waves are clearly evident on all three axes.

Figure 6

Figure 6 - This figure shows the same data as in figure 3, except now the low-pass filter has a period of 20 seconds (0.05 Hz). The surface waves are still clearly evident on all three axes.

Figure 7

Figure 7 - This figure shows the same data as in figure 3, except now the low-pass filter has a period of 50 seconds (0.02 Hz). At this frequency, some ground motion is still visible.

We designed the Atom to be used in a number of engineering applications, the most notable being microseismic monitoring in oil-fields, engineering hazard studies and other applications where having small, reliable, and wireless seismic instruments are beneficial. Earthquakes are typically recorded using seismometers, and vast networks of these instruments cover the globe and are used for a variety of tasks. The most obvious is earthquake detection and monitoring as well as early warning systems, but can also be used in military and security applications. However, the Atom is sensitive enough to use as an inexpensive and portable seismometer for the same tasks. An Atom would be ideal for classrooms or for use in smaller studies where budgets don’t allow for purchasing a traditional seismometer. If you have questions about the Atom or any of our other seismic products, please contact us at Sales.

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