# Slow earthquake study relies on fast digital data

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Several weeks ago, we reported on the anticipated Kīlauea slow earthquake - a very interesting and recently recognized component of our volcano's evolution. Unfortunately, the slow earthquake did not comply with our expectations, and we continue to wait for it with both our permanent monitoring networks and the temporary instruments that we deployed in February.

Anticipated Kīlauea volcano's "slow earthquake" location.
Image courtesy of NASA.

(Public domain.)

Studies like our Kīlauea slow earthquake project provide terrific opportunities to work somewhat differently than in our routine volcano and earthquake monitoring mode. In this case, we were able to borrow and deploy a type of seismometer that we hope to add to our Hawaiian Volcano Observatory's (HVO) permanent seismic monitoring tool kit.

Our current earthquake monitoring network is made up of sensors whose signals are radioed to HVO in analog form, then digitized on two computers. These newer seismometers are designed to produce their data in digital form right at the sensor. As with digital music and television, this reduces the possibility of loss of data quality in the sometimes long radio trip back to HVO.

With additional electronics at the remote stations, the digital seismometers can be configured to record a wider range of seismic frequencies and increase the range of earthquake magnitudes that we can analyze. Our permanent network affords a very narrow view (black and white) into the wide range of seismic signals that earthquakes generate (full color).

Because the data from the newer instruments is digital in form, it can be brought back to HVO via several technologies, including the Internet and digital radio. If successful, we can view and analyze the data continuously and in real time. If communication links fail, the data are stored on site. When communication is restored, we can retrieve the data that would otherwise have been lost.

In the case of our slow earthquake chase along Kīlauea's south flank, we are not sending anything to HVO and must manually retrieve the data. Not a problem. As visitors to Hawaii Volcanoes National Park can attest, this is done by hiking on wonderful trails in one of the world's most incredibly scenic settings. The data can be downloaded on site and/or data cards can be swapped.

Following the December 2004 Sumatra and 2006 Kiholo Bay earthquakes, we are working with our Pacific Tsunami Warning Center (PTWC) and U. S. Geological Survey (USGS) National Strong Motion Project (NSMP) monitoring partners to upgrade our seismic networks in Hawaii to include a much larger number of real-time digital seismic sensors.

Along with the new instruments being installed around the islands, it is also important that we improve and expand upon our collection of analytical tools to take advantage of the improved data quality.

The PTWC is striving to compute reliable earthquake magnitudes and report them within 90 seconds of the earthquake. Likewise, the USGS is committed to rapid and reliable earthquake analysis and reporting. In addition, the USGS is committed to posting information relating to earthquake damage and earthquake hazards, like the ShakeMap and Community Internet Intensity Maps (CIIM) that we have mentioned in earlier Volcano Watch reports. We would also like to compute more detailed faulting and slip models of large earthquakes.

We greatly appreciate the community interest that allows the posting of Hawaii CIIM. The Kiholo Bay ShakeMap was posted almost a day after the earthquake. We are hoping to be able to automatically compute and post a ShakeMap, minutes after an earthquake. Recent and planned upgrades to PTWC and USGS stations in Hawaii are critical to meeting our performance goals. In the meantime, while waiting for our slow earthquake, we?re able to get better acquainted with the seismic tools of our future.

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### Volcano Activity Update

This past week, activity levels at the summit of Kīlauea Volcano have remained at background levels. The summit caldera has been expanding, indicating inflation, since the beginning of 2007. The number of earthquakes located in the summit area is at low levels (usually fewer than 10 per day are large enough to locate). There have been local concentrations of earthquakes beneath the summit area.

Eruptive activity at Puu Oo continues, though the level of activity seems somewhat subdued compared to the last few years. On clear nights, glow is visible from three vents within the eastern half of the crater. Lava is still flowing through the PKK lava tube, and unusual activity along the uppermost portion of the tube has built new hornitos there. The PKK tube continues to carry some lava to the top of Pulama pali, where a small breakout has been active for weeks. Most of the lava, however, is going into the Campout tube that branches off from the PKK tube about 1 km south of Puu Oo. The Campout tube carries lava to the ocean at Kamokuna located inside Hawaii Volcanoes National Park.

For the past week on the flow field, streams of lava from the Campout flow have been seen daily descending Pulama pali. Scattered breakouts also remain active from near the base of the Royal Gardens subdivision to within several hundred meters of the coast. The laze plume created by the ocean entry at Kamokuna remains small, suggesting that little lava is entering the water.

Access to the sea cliff near the ocean entries is closed, due to significant hazards. The surrounding area, however, is open. If you visit the eruption site, check with the rangers for current updates, and remember to carry lots of water when venturing out onto the flow field.

No earthquakes beneath Hawaii Island were reported felt within the past week.

Mauna Loa is not erupting. Two earthquakes were located beneath the summit. Extension of distances between locations spanning the summit, indicating inflation, continues at steady, slow rates.