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Volcanowatch

September 27, 2007

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.


Progress in the year following the Kiholo Bay earthquake

 USGS/ANSS ShakeMap product showing instrumental shaking intensities estimated for the magnitude-5.4 Kilauea south flank earthquake on August 13, 2007 at 7:38 p.m. Hst.
USGS/ANSS ShakeMap product showing instrumental shaking intensities estimated for the magnitude-5.4 Kilauea south flank earthquake on August 13, 2007 at 7:38 p.m. Hst.

This coming October 15 will mark one year since last October?s damaging earthquakes that rocked Hawai`i County. To briefly recall them, at 7:07 AM on Sunday, October 15, 2006, a magnitude 6.7 earthquake ruptured the Earth?s lithosphere about 40 km (24 miles) beneath Kiholo Bay. Just 7 minutes later, a magnitude 6.0 earthquake occurred offshore of Mahukona, 20 km (12 miles) deep.

Beyond being simple reminders that we can expect large earthquakes here, last October?s earthquakes compelled us to live and work through actual events that had real consequences. Though economic losses were certainly substantial, it could be argued that, perhaps because of the time of day and day of the week, Hawai`i County might have dodged far more serious impact. What if the earthquakes occurred during the ?rush hour,? or with students at school and many others at work? What if the earthquakes had occurred closer to more heavily populated areas like Hilo or Kailua?

Through the National Earthquake Hazards Reduction Program, the United States Geological Survey (USGS), the Federal Emergency Management Agency, the National Science Foundation, and the National Institute of Standards and Technology are the four Federal agencies charged by Congress to reduce the risks of life and property from future earthquakes. The USGS is responsible for earthquake monitoring and reporting.

The USGS Advanced National Seismic System (ANSS) project was formed a number of years ago, both to modernize and to coordinate earthquake monitoring in the United States. There is a Hawai`i Region identified in the ANSS, but it has not been an area of ANSS focus because our greatest seismic hazards do not lie within an ?urban? setting.

While our focus at the Hawaiian Volcano Observatory (HVO) is on volcano monitoring and research, HVO also plays an important role in the USGS?s earthquake monitoring. During the past year, we have evaluated the performance of HVO and other parts of the USGS responding to the Kiholo Bay and Mahukona earthquakes, with the aim of improving our responses to future earthquakes.

Considerable investments have been made in seismic monitoring in Hawai`i, and we strive to coordinate our resources constructively and strategically to afford clear, concise, and reliable reports about our earthquakes.

To be sure, improvements can be made to our technical capabilities, including new instruments, new computer systems, and new data analysis techniques. With new technologies, exciting possibilities need to be explored and, possibly, implemented. We have identified shortcomings where improved Internet connectivity and important data from planned systems will help greatly ? even in terms of simply generating more reliable earthquake locations and magnitudes.

As a result of several meetings and discussions since last October's earthquakes, we've already made important progress, for example, in producing ShakeMaps, near real-time maps of the intensity of shaking produced by earthquakes. For the October 2006 quakes, the ShakeMaps were posted well after the earthquakes had occurred and were based on only 12 strong-motion instruments and the results from the community-contributed Did-You-Feel-It? maps.

Twelve additional strong-motion systems have now been upgraded to automatically send their data to the ShakeMap systems and more are scheduled. ShakeMaps are now generated somewhat automatically using this expanded set of data and the resulting ShakeMaps for Hawai`i earthquakes can be found at http://earthquake.usgs.gov/eqcenter/shakemap.

While last October reminded us of Hawai`i?s history of damaging earthquakes, there is still an element of ?unexpectedness? when one strikes. As we await our next one, we'll be working to implement and operate our upgraded systems to provide the broad range of ANSS products to emergency managers and the general public. We hope that these will help in framing earthquake and emergency response plans to mitigate against potential losses and casualties. For additional information: http://earthquake.usgs.gov

Activity update

Kilauea summit and Pu`u `O`o continued to deflate. Seismic tremor levels continued to be low. Earthquakes were located beneath Halema`uma`u Crater, the south flank area, and the lower southwest rift zone.

The July 21 eruption remains active. The erupting lava flows through an open, perched lava channel about 1.4 km (0.9 miles) long and can be naturally divided into four distinct wide sections separated by constrictions, two of which are roofed over. At the end of the perched channel, the lava turns sharply east and cascades into a lower channel. The lower channel is about 600 m (~2000 ft) long, and disappears as it transitions into an `a`a flow.

The `a`a flow fed by the lower channel has been reburying older `a`a flows erupted in August and have only reached about 1.8 km (1.1 miles) beyond the end of the lower channel. As of Thursday, September 27, the lower channel had spawned a new `a`a flow that was heading south toward the southern margin of the flow field.

At Pu`u `O`o, no incandescence has been seen on the Webcam at night for the last several weeks. The heavy fume coming from Pu`u `O`o completely obscures any view into the crater. As has been seen in years past, Pu`u `O`o could be acting as temporary storage for lava that passes beneath the cone on its way to the erupting fissure. It is, basically, a big chimney. There have also been a number of collapses in Pu`u `O`o crater since late August, and numerous fresh cracks cut the north rim and south flank of the cone.

At Pu`u `O`o, no incandescence has been seen on the Webcam at night for the last few weeks. The heavy fume coming from Pu`u `O`o completely obscures any view into the crater. As has been seen in years past, Pu`u `O`o could be acting as temporary storage for lava that passes beneath the cone on its way to the erupting fissure. There have also been a number of collapses in Pu`u `O`o crater since late August, and cracks on the north rim and south flank of the cone seem to be widening.

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).

Two earthquakes beneath Hawai`i Island were reported felt within the past week. A magnitude-3.1 earthquake occurred at 7:32 p.m. on Sunday, September 23, 2007 HST and was located 16 km (10 miles) east of Hawi at a depth of 34 km (21 miles). A magnitude-2.7 earthquake occurred at 8:15 p.m. on Wednesday, September 26, and was located 16 km (10 miles) southeast of Mauna Loa summit at a depth of 11 km (7 miles).

Mauna Loa is not erupting. No earthquakes were located beneath the summit. Extension between locations spanning the summit, indicating inflation, continues at steady, slow rates, which have slowed further since May 2007.

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


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Updated: October 1, 2007 (pnf)