Volcano Tectonic & Long Period Event Classification from Eruptions

Sadia Marium Rinty, & Thomas H. Goebel

Published September 8, 2024, SCEC Contribution #13660, 2024 SCEC Annual Meeting Poster #017

The complex geometry and rupture processes during volcanic eruptions produce different types of seismicity e.g., volcano-tectonic (VT), long-period events (LP), tremors, tornillos, and hybrid events. Volcano tectonic events are generated from the brittle failure of rocks, while long periods are due to a slow rupture and slip velocities, often associated to fluid-related processes (Thomas et al., 2016; Wang et al. 2023; Chouet 2003; Woods et al. 2018). Classifying these signals is crucial for understanding the underlying processes during an eruption cycle.
VT events have dominant P and S wave arrivals, with frequency range between 10 to 30 Hz. Long period events are depleted in high-frequency content, with a dominant frequency range 5 to 10Hz. The source parameters are also distinct. LPs have a lower corner frequency, and two to three orders of lower stress drop when compared to an earthquake of the same size (Wang et al. 2023). We are motivated to classify VT and LP from eruption seismicity by utilizing these differences in their source attributes and spectral signature.
We analyze seismicity associated with major eruption sequence of Kilauea, Hawaii; Okmok and Akutan, Alaska. We utilize the seismicity catalog by USGS for the 2018 Kilauea eruption sequence, relocated seismicity catalog by Garza-Girón et al. (2023) for 2008 Okmok eruption and relocated catalog by Power et al. (2019) for Akutan.
We calculate power spectra and spectral ratios from waveforms for all cataloged events at all available stations using multitaper method. Then we compute energy ratio (ER) and frequency index (FI) for each event. The histograms of ER and FI of events show a bimodal distribution, which indicates two distinct types of events. Based on the bimodal distribution, we define a boundary value to classify VT & LPs.
To understand the efficiency of ER & FI regardless of eruption types, we apply the method on synthetic VT & LP. The principle of creating synthetic VT & LP is based on their distinguished source parameter attributes. We apply a Brune-type source pulse, using a random log-normal distribution of stress drop, where VT events have three orders of magnitude higher stress drop than LP events. The two different populations of source pulses for VT & LP are then convolved with similar path & site terms for generating synthetic waveforms. The scope of this research is to develop a methodology for classifying VT & LP events regardless of any particular eruption type.

Key Words
Volcano Seismicity, Long Period Events, Volcano Tectonic Events, Synthetic Waveforms

Citation
Rinty, S., & Goebel, T. H. (2024, 09). Volcano Tectonic & Long Period Event Classification from Eruptions . Poster Presentation at 2024 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology