Broadband Seismometer to Tilt Conversion for Monitoring Kīlauea Volcano
Abstract:Tilt transients are common at active volcanoes and potentially mark magma and gas movements in a frequency band between GPS and typical broadband seismometers. Tiltmeters record such signals, but for optimal sensitivity, require a borehole installation, which especially restricts their use in remote or culturally sensitive areas. The summit of Kīlauea Volcano hosts a network of 4 tiltmeters within 5 km of the summit vent, but none within 2 km because of the culturally sensitive nature of Kīlauea Caldera. The almost equidistant configuration of the tilt network limits the ability to resolve the depth of the source of tilting, and the distance from the source limits the resolution of near-surface events, such as those associated with processes affecting the lava lake. There is, however, an 11 station broadband seismometer network within 5 km of the summit vent, with 5 stations within 2 km. Data from these seismometers can be converted to tilt to augment the existing tiltmeter network. This improved network of tiltmeters and seismometers has the potential to support detailed modeling of processes operating on the timescale of hours to a day. We develop a set of parameters to enable the transform of velocity to tilt in near-real-time for use in volcano monitoring and rapid modeling. We also investigate the use of recursive filtering to rapidly and efficiently transform a streaming broadband signal to tilt and enable its near-real time interpretive utility.
We look at a variety of signals, including crater rim collapses, very long period earthquakes, long period earthquake swarms and lava lake overflows in order to better understand the sensitivity of the broadband seismometers to different frequencies of tilt. To validate the transform from velocity to tilt, especially the amplitude, we examine two collocated tiltmeter-broadband seismometer stations. In general, the broadband seismometer network has more sensitivity to minor tilt transients because of its proximity to the tilt source.