Kiholo Bay Aftershocks - Thumping for Science

Release Date:

As we greet our new year at the U S Geological Survey's (USGS) Hawaiian Volcano Observatory (HVO), we take a look back at the Kīholo Bay earthquakes.

Kiholo Bay Aftershocks - Thumping for Science...

George E. Brown, Jr. Network for Earthquake Engineering Simulation mobile shaker "Thumper," a modified Ford F650 truck equipped with hydraulic pumps and shakers. Thumper operates at frequencies between 17 and 225 cycles per second, and is capable of generating a maximum force of 6000 pounds. Photo from http://nees.utexas.edu/Equipment-Thumper.shtml

(Public domain.)

Still quite real and prominent in many minds is the October 2006 magnitude 6.7 Kīholo Bay sequence of earthquakes. The Mauna Kea Beach Resort remains closed because of earthquake damage, and Hāmākua drivers still wind their way through the Pa‘auilo Bridge detour.

From October 2006 through the end of 2007, HVO's seismic data analysts cataloged nearly 400 aftershocks from the Kīholo Bay source region. Typical of earthquake sequences, the majority of aftershocks occurred soon after the mainshock. Eighty percent of the Kīholo aftershocks occurred between October 15 and December 31, 2006.

As the aftershocks tapered off through 2007, though, the earthquakes have led to other activities. Last year, a number of follow-up projects were initiated to improve our understanding of how earthquakes affect us.

After a potentially devastating event like a big earthquake, it is becoming the practice, if not the policy, of the Federal Emergency Management Agency (FEMA) to use a computer program called HAZUS to project estimated losses and casualties due to the event. Indeed, right after the earthquake, FEMA's HAZUS expert in Denver was notified and he produced a HAZUS model for Kīholo Bay to help FEMA and other earthquake responders size up the situation.

HAZUS uses prescribed census, building, infrastructure and other information, as well as input data about the earthquake, to make its projections. FEMA very clearly understands that, as with all other computer programs, the HAZUS output is only as good as the HAZUS input, and FEMA has started a project to use information collected after the Kīholo earthquakes to see how it can better tune its HAZUS projections for future earthquakes in Hawai‘i.

Closely related to the HAZUS calibration project are 2 new geophysical studies. They both focus on strong motion instruments operated by the USGS in Hawai‘i to record the shaking caused by large earthquakes without going off-scale.

Strong motion data are central to understanding the physics of large earthquakes. More practically speaking, they are also important for calculating earthquake magnitudes and for creating USGS earthquake information products called the National Seismic Hazards Map (http://earthquake.usgs.gov/research/hazmaps/products_data/index.php) and ShakeMap (http://earthquake.usgs.gov/eqcenter/shakemap/).

Seismic signals, including strong motion data, are affected by how seismic energy weakens as seismic waves travel from earthquake to instrument site. In addition, shallow geologic conditions immediately beneath the instrument site can cause strong variations in strength of shaking.

For Hawai‘i, both the hazard map and ShakeMap use data collected before 2006. Thankfully, large earthquakes are relatively infrequent, but this also means that these products were built using available data without the benefit of including deep earthquakes like Kīholo Bay or data from the entire USGS strong motion network operated on Hawai‘i.

One of the new projects will study the strong motion records from last October and compare these to the older datasets. This will help in the development of a Hawai‘i-specific attenuation relation for deep earthquakes, and, thus, in a planned USGS update of the seismic hazards map for Hawai‘i.

The other new project, while promising to be as valuable as the attenuation study, also offers some excitement and hopefully even some fun.

This week, a truck named "Thumper" arrives from the George E. Brown, Jr., Network for Earthquake Engineering Simulation (NEES) facility at the University of Texas. NEES is a consortium funded by the National Science Foundation to promote earthquake research.

Thumper is the junior member of a family of truck-mounted shakers including "T-rex" and "Liquidator." Over the course of the next two weeks, Thumper will visit all of the USGS strong motion sites from Kawaihae to Mauna Kea to measure the effects of local site geology.

As you might guess, once set up, Thumper will simply shake the ground like an earthquake would but under controlled conditions. Thumper's data will be used to improve both the Hawai‘i hazards map and ShakeMap. Please drive safely anyway, but be on the look out for 11 tons of NEES shaker.

Again, Happy New Year from HVO!

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Volcano Activity Update

Kīlauea summit and Pu‘u ‘Ō‘ō continued to deflate. Seismic tremor levels at the summit are elevated but are still at low levels. Summit sulfur dioxide emissions have also increased. Earthquakes were located mostly beneath Halema‘uma‘u Crater and the south flank faults.

On July 21, 2007, lava began erupting from a set of fissures on the east flank of Pu‘u ‘Ō‘ō. Eruptive activity soon stabilized at fissure D, 2.3 kilometers (1.4 mi) northeast of Pu‘u ‘Ō‘ō. For the last several months this lava was directed entirely into a perched channel, consisting of separate pools often separated by bridges of cooled lava. At dawn on November 21, lava began to erupt directly from fissure D, outside of the perched channel, creating the Thanksgiving Eve breakout (TEB) flow. Lava supply to the original perched channel has been, in part, redirected through this new outlet, cutting off supply to the eastward tube which had been feeding flows in the vicinity of Pu‘u Kia‘i through much of November.

The TEB flow has continued to build itself vertically and laterally over the last several weeks. During this past week the front of active TEB lava has advanced approximately 500 meters (or yards), with the currently active flow front reaching a distance of 2 km (1.2 mi) southeast of fissure D. The TEB flow consists of a primary shield over the fissure, with several rootless shields along a line towards the southeast. Just north of the TEB flows, the perched channel and its extensive seeps have been completely inactive for the past week.

Minor incandescence in Pu‘u ‘Ō‘ō has been observed a few times since early December, but has otherwise been absent since Aug. 31. As in years past, Pu‘u ‘Ō‘ō likely is serving as a large chimney, beneath which lava is stored briefly and degassed substantially enroute to the erupting fissure. Sloughing of Pu'u 'O'o into its own crater since late August has left numerous fresh cracks on the north rim and south flank of the cone.

Vent areas are hazardous. Access to the eruption site, in the Pu‘u Kahauale‘a Natural Area Reserve, is closed (http://www.state.hi.us/dlnr/chair/pio/HtmlNR/07-N076.htm).

Five earthquakes beneath Hawai‘i Island were reported felt within the past week. A magnitude-2.4 earthquake occurred at 9:52 p a.m. H.s.t. on Thursday, December 27, 2007, and was located 6 km (4 miles) west of Pāhala at a depth of 6 km (4 miles). A magnitude-2.8 earthquake occurred at 7:04 a.m. on Saturday, December 29, and was located 2 km (1 mile) northwest of Waiki‘i at a depth of 17 km (10 miles). A magnitude-2.8 earthquake occurred at 3:40 p.m. on Sunday, December 30, and was located 20 km (13 miles) southwest of Kawaihae at a depth of 10 km (6 miles). A magnitude-2.4 earthquake occurred at 7:49 p.m. on Monday, December 31, and was located 8 km (5 miles) northeast of Kukuihaele at a depth of 36 km (22 miles). A magnitude-3.3 earthquake occurred at 7:21 p.m. on Tuesday, January 1, 2008, and was located 6 km (4 miles) south of Pu‘u ‘Ō‘ō Crater at a depth of 10 km (6 miles)

Mauna Loa is not erupting. Three earthquakes were located beneath the summit. Extension between locations spanning the summit, indicating inflation, continues at steady, slow rates. The Mauna Loa webcam radio transmitter is buried in snow and is not operational.

Visit our Web site for daily Kīlauea eruption updates and nearly real-time Hawai‘i earthquake information. Kīlauea daily update summaries are also available by phone at (808) 967-8862. skip past bottom navigational bar