An approach to source characterization of tremor signals associated with eruptions and lahars

Abstract

Tremor signals are observed in association with eruption activity and lahar descents. Reduced displacement (D R ) derived from tremor signals has been used to quantify tremor sources. However, tremor duration is not considered in D R , which makes it difficult to compare D R values estimated for different tremor episodes. We propose application of the amplitude source location (ASL) method to characterize the sources of tremor signals. We used this method to estimate the tremor source location and source amplitude from high-frequency (5-10 Hz) seismic amplitudes under the assumption of isotropic S-wave radiation. We considered the source amplitude to be the maximum value during tremor. We estimated the cumulative source amplitude (I s ) as the offset value of the timeintegrated envelope of the vertical seismogram of tremor corrected for geometrical spreading and medium attenuation in the 5-10-Hz band. For eruption tremor signals, we also estimated the cumulative source pressure (I p ) from an infrasonic envelope waveform corrected for geometrical spreading. We studied these parameters of tremor signals associated with eruptions and lahars and explosion events at Tungurahua volcano, Ecuador. We identified two types of eruption tremor at Tungurahua: noise-like inharmonic waveforms and harmonic oscillatory signals. We found that I s increased linearly with increasing source amplitude for lahar tremor signals and explosion events, but I s increased exponentially with increasing source amplitude for inharmonic eruption tremor signals. The source characteristics of harmonic eruption tremor signals differed from those of inharmonic tremor signals. We found a linear relation between I s and I p for both explosion events and eruption tremor. Because I p may be proportional to the total mass involved during an eruption episode, this linear relation suggests that I s may be useful to quantify eruption size. The I s values we estimated for inharmonic eruption tremor were consistent with previous estimates of volumes of tephra fallout. The scaling relations among source parameters that we identified will contribute to our understanding of the dynamic processes associated with eruptions and lahars. This new approach is applicable in analyzing tremor sources in real time and may contribute to early assessment of the size of eruptions and lahars.

Calibrating the amplitude source location (ASL) method by using active seismic sources: An example from Te Maari volcano, Tongariro National Park, New Zealand

“…AFs have been applied successfully at some volcanoes, i.e., Cotopaxi, Ecuador [ Kumagai et al , ] and Miharayama, Japan [ Ogiso and Yomogida , ], while at others, Tungurahua, Ecuador [ Kumagai et al , ] and Te Maari, New Zealand (Figure a), AFs actually impair the location quality. This has led to Kumagai et al [] forgoing site amplification factors in determining locations at Tungurahua. The AF sensitivity analysis completed here (Figure b) suggests that such corrections may introduce significant uncertainties into the location process.…”

Seismic and acoustic signatures of surficial mass movements at volcanoes

“…ASL has been used for the location and tracking of lahars and debris flows (Kumagai et al, 2015(Kumagai et al, , 2010(Kumagai et al, , 2009Ogiso and Yomogida, 2015;Walter et al, 2017), rock falls (Battaglia and Aki, 2002), and pyroclastic flows (Yamasato, 1997;Jolly et al, 2002). Similar to most of the techniques described here, ASL has only been used as a post-event research and proof-of-…”

Seismic Amplitude Ratio Analysis of the 2014–2015 Bárarbunga‐Holuhraun Dike Propagation and Eruption

“…The amplitude source location method was originally proposed by Battaglia and Aki () to overcome the limitations of traditional methods to locate earthquakes. It has already been applied successfully to locate various volcano‐seismic signals (Battaglia, Aki, & Ferrazzini, ; Battaglia, Aki, & Staudacher, ; Eibl et al, ; Kumagai et al, , , , , ; Kurokawa et al, ; Ogiso & Yomogida, , ; Ogiso et al, ) using high‐frequency seismic amplitudes and assuming isotropic radiation of S waves. A grid search is usually conducted to find a source location that provides the best fit between observed envelope amplitudes corrected for site amplification factors at individual stations and calculated amplitudes using the far‐field S wave equation with isotropic radiation (Morioka et al, ).…”