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Seismically-Derived Ground Tilt From Rainfall-Triggered Lahars at Volcán De Fuego, Guatemala

Description: 

Broadband seismometers deployed for lahar detection may also respond to load-induced ground rotation near the lahar channel. We analyzed tilt signals on two permanent and four temporary broadband stations deployed along two active secondary lahar channels on the flanks of Volcán de Fuego, Guatemala over parts of three years. These rainfall-triggered lahars occur mainly between May and October and have durations from 30 minutes to 6 hours. Seismic stations were located at distances from 10 to 350 m from the channels and have corner frequencies at 60 or 120 seconds. These deployments were designed for lahar detection at relatively high frequencies at which lahars are most energetic. The seismograms exhibit clear signals below the instrument corners that suggest the lahar masses produce rotation at the stations. We began with a catalog of lahars for years 2021-2023. For each lahar, tilt was derived using a standard approach for signals below the instrument corner: integrating the raw signal; applying a low-pass filter below the instrument corner; and multiplying by a scale factor. The derived tilt signals are fairly complex and vary between stations within a single drainage for a given lahar event. Typical signals have a relatively sharp onset followed by multiple pulses within a single lahar event which are generally consistent with the timing of later flow surges as indicated by the high-frequency seismicity. The tilt particle motions are not necessarily perpendicular to the channel and are often elliptical. Finite-difference modeling using a UAS-derived high-resolution DEM suggests topographic effects produce mismatches between back-azimuth and particle motion direction of 10-25º. In a small number of cases, we combine time-lapse camera images with the lahar records to estimate the lahar masses. This study builds on earlier work that demonstrates the utility of broadband seismometers as tiltmeters in a variety of natural settings.

Session: Detecting, Characterizing and Monitoring Mass Movements [Poster Session]

Type: Poster

Date: 5/2/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Gregory

Student Presenter: No

Invited Presentation: 

Authors