Netquakes and Shakemaps—How you can get involved in HVO seismology

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On October 19, 2011, a magnitude-4.5 earthquake struck on the northwest flank of Mauna Kea at 2:10 p.m., HST, followed by more than 50 aftershocks over the next 24 hours. More than 500 people reported feeling the main quake on the "Did you feel it" webpage.

Netquakes and Shakemaps—How you can get involved in HVO seismology ...

This USGS Shakemap (http://earthquake.usgs.gov/earthquakes/shakemap/hv/shake/60276536/) is a model for the shaking that occurred during the magnitude-4.5 earthquake on October 19, 2011. Circles and triangles show locations of the seismometers that were used to model the shaking, with warm colors indicating more shaking than cool colors.

(Public domain.)

The earthquake is an example of one of most common types of seismicity throughout the Hawaiian Islands—seismicity associated with the breakdown of the island.

Throughout geologic time, volcanic forces have constructed the Hawaiian Islands, while gravity has acted to degrade them. If the islands behaved like plastic, gravity’s effects would be uniform in time and space. Because the islands we live on are brittle, however, their breakdown occurs piecemeal along faults, cracks in the Earth's crust. Large faults can produce large earthquakes, such as the 1975 Kalapana earthquake and 2006 Kīholo Bay earthquake. In the past 100 years, many large earthquakes on and around the Hawaiian Islands can be attributed to structural adjustments associated with the breakdown of the islands.

Whereas last week's magnitude-4.5 earthquake caused no reported damage, larger earthquakes, such as the magnitude-6.7 Kīholo Bay quake in 2006, do have the potential to cause widespread damage to structures and personal property. Following a large earthquake, emergency responders benefit from knowing which areas experienced the most shaking so that resources can be focused on those areas that sustained the greatest damage. Such information is difficult, if not impossible, to glean from people in the affected areas because of the telephone and power outages that commonly occur shortly after an earthquake.

While seismologists can estimate shaking potential within minutes of an earthquake, variations in surface geology can render such models inadequate unless they are tied to actual measurements of shaking. The more measurements seismologists have, the more accurate the model of shaking can be and the more effective that model is for gauging damage potential.

The Hawaiian Volcano Observatory (HVO), with our partners at the Pacific Tsunami Warning Center and National Strong Motion Program, operate a network of strong-motion seismometers across the Hawaiian Islands. These seismometers are specially designed to record large ground motions. Currently there are 69 strong-motion sensors installed on the islands of Hawai‘i (50) Maui (6), Moloka‘i (2), O‘ahu(8), Lāna‘i (1) and Kaua‘i (2).

A new strong-motion sensor, which is both inexpensive and technologically advanced, was recently developed. These instruments use household wireless networks (WiFi) to transfer their data to a central data center when an earthquake is detected. Extensive networks of these new sensors, called Netquakes, have been installed in many places in the United States, especially California and Washington (http://earthquake.usgs.gov/monitoring/netquakes/map/).

HVO has installed 5 Netquakes on the Island of Hawai‘i and expects to install additional instruments in areas not already covered by the existing permanent network. These include areas south of Hilo and the northeast and western coasts of the Island of Hawai‘i, as well as anywhere on the Island of Maui, and urban and suburban areas of Honolulu on the island of O‘ahu.

Residents interested in potentially hosting a Netquakes instrument need a concrete pad on which the seismometer can be installed, a permanent broadband network connection, and AC power to operate the seismometer. The instruments use little bandwidth and typically do not use enough power to noticeably increase electric bills. A seismologist occasionally has to replace the internal battery or troubleshoot the connection to the seismometer, but this usually requires less than one visit per site per year.

If you'd like to volunteer to host a Netquake seismometer and have a site that meets the above requirements, please fill out the form at https://sslearthquake.usgs.gov/monitoring/netquakes/signup/hawaii/. If your site is selected for a Netquakes instrument, it will be placed on the current Netquakes map and data from your seismometer can be viewed through the web interface at http://earthquake.usgs.gov/monitoring/netquakes/map/hawaii/.

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Volcano Activity Update

A lava lake was present within the Halema‘uma‘u Overlook vent over the past week, resulting in night-time glow that was visible from the Jaggar Museum overlook. The lake, which is about 100 m (328 ft) below the floor of Halema‘uma‘u and visible by Webcam, rose and fell slightly during the week in response to a series of small deflation-inflation cycles.

Activity on Kīlauea's east rift zone was restricted to surface flows about 2.5 km (1.5 miles) east-southeast of Pu‘u ‘Ō‘ō. These flows travel through a lava tube that is fed by the September 21 fissure on the upper east flank of the Pu‘u ‘Ō‘ō cone.

No earthquakes beneath Hawai‘i Island were reported felt this past week.