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Insights on Multistage Rock Avalanche Behavior From Runout Modeling Constrained by Seismic Inversions

Journal of Geophysical Research: Solid Earth

October 2022
127(10)

DOI:10.1029/2021JB023444

Authors:

Andrew Mitchell

BGC Engineering Inc.

Show all 7 authorsHide

Inversion of low‐frequency regional seismic records to solve for a time series of bulk forces exerted on the earth by a landslide (a force‐time function) is increasingly being used to infer volumes and dynamics of large, highly energetic landslides, such as rock avalanches and flowslides, and to provide calibration information on event dynamics and volumes for numerical landslide runout models. Much of the work to date using landslide runout modeling constrained by seismic data has focused on using single‐phase models with frictional or velocity‐weakening rheologies. Awareness of multistage landslide initiations is increasing, with discrete failures separated in time contributing to the final impact of an event. Our work utilizes a method for incorporating seismic data as a calibration constraint for landslide runout models, considering variable rheologies and different initiation conditions. This study presents a systematic examination of multiple rheologies and initiation conditions, and shows how these factors affect the force‐time function derived from the landslide runout model. Our work confirms that, while rheology and fragmenting or initially coherent initiations affect the force‐time function, multiple collapses separated by tens of seconds have the greatest impact on the shape and amplitude. We apply this method to the analysis of three real rock avalanches to better constrain plausible initiation conditions and rheology parameters using both seismic and field data. This study provides insights on how assumptions about the initiation dynamics of the source zone and the runout model definition can aid in the interpretation of seismic inversions for multistage rock avalanches.

Comparison of Voellmy, Bingham, and undrained Voellmy model results for the idealized topography calibrated to a frictional case (base case) with φb = 15°. Total impact area for the frictional case is indicated by the red outline on all panels. (a) Topographic profile and initial position of the source material (in orange) along Y = 0. Total impact area and final deposit for (b) frictional, (c) Voellmy, (d) Bingham, and (e) undrained Voellmy. Gray background lines show elevation contours, in meters, with major contours at a 500 m interval.

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Comparison of the simulated total impact area with φb = 15° for single‐stage initial conditions (black lines) as the base case compared to the three other initiation condition scenarios considered (red, blue, and purple lines). (a) Failure over 10 s, (b) failure over 20 s, and (c) failure over 30 s. Gray background lines show elevation contours, in meters, with major contours at a 500 m interval. A section view of the source volume entering the model in a two‐stage initiation, (d) where half the mass is initialized at 0 s (dark red), (e) which then travels downslope, and (f) the second half of the material is initialized at rest (orange).

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Band‐pass filtered (15–250 s) model forces from: single‐stage Frictional, Voellmy, Bingham, and undrained Voellmy simulations (a and b) shown in Figure 1; two‐stage initiation (c and d); fragmenting initiation (e and f); and initial coherence simulations (g and h) shown in Figure 2.

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Locations of the three case histories, (a) Bingham Canyon Mine, Utah, USA; (b) West Salt Creek, Colorado, USA; (c) Joffre Peak, British Columbia, Canada. Inset imagery—Planet Inc. (2021).

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Bingham Canyon Mine multistage failure force‐time functions comparing best‐fit inversion to the calibrated DAN3D frictional parameters and coherent block initiation from Aaron et al. (2017) (labeled original calibration) with a two‐part failure occurring over 10 s for Event 1 and a three‐part failure occurring over 30 s for Event 2. The start of each failure stage is indicated by the vertical dashed lines (a–c and e–g). Panels (d) and (h) show the impact area and final deposit for the maximum likelihood Bingham Canyon Mine multistage failure models, respectively. Note: model coordinate 0, 0 corresponds to 401508.868 E, 4485666.303 N, and UTM Zone 12T (40°30’57.157” N and 112°09’45.433” W).

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1. Introduction

Extremely rapid, large, flow-like landslides (as defined by Hungr etal.,2014) are among the most catastrophic

natural hazards on Earth. These landslides are characterized by a deficit between driving and resisting stresses

at the initiation of motion, which results in rapid acceleration. This deficit is gradually reduced during motion

through traction stresses, plastic deformations, heat, and sound, among other forms of energy dissipation, until

the potential energy of the landslide has been fully consumed (Knapp & Krautblatter,2020). If a landslide is

sufficiently large and rapid, the vibrational energy imparted on the earth can be measured by seismographs, with

different landslide types having distinct signal characteristics (e.g., review papers by Allstadt etal., 2018 and

Provost etal.,2018, and references therein). Many of the most seismically energetic landslides are classified as

Abstract Inversion of low-frequency regional seismic records to solve for a time series of bulk forces

exerted on the earth by a landslide (a force-time function) is increasingly being used to infer volumes and

dynamics of large, highly energetic landslides, such as rock avalanches and flowslides, and to provide

calibration information on event dynamics and volumes for numerical landslide runout models. Much of the

work to date using landslide runout modeling constrained by seismic data has focused on using single-phase

models with frictional or velocity-weakening rheologies. Awareness of multistage landslide initiations is

increasing, with discrete failures separated in time contributing to the final impact of an event. Our work

utilizes a method for incorporating seismic data as a calibration constraint for landslide runout models,

considering variable rheologies and different initiation conditions. This study presents a systematic examination

of multiple rheologies and initiation conditions, and shows how these factors affect the force-time function

derived from the landslide runout model. Our work confirms that, while rheology and fragmenting or initially

coherent initiations affect the force-time function, multiple collapses separated by tens of seconds have the

greatest impact on the shape and amplitude. We apply this method to the analysis of three real rock avalanches

to better constrain plausible initiation conditions and rheology parameters using both seismic and field data.

This study provides insights on how assumptions about the initiation dynamics of the source zone and the

runout model definition can aid in the interpretation of seismic inversions for multistage rock avalanches.

Plain Language Summary Understanding how large, rapid landslides move is important to

estimate the dangers posed by these events. Large, rapid landslides impart forces on the surface of the earth

when they accelerate during their initial movement, when they change direction as they follow the terrain along

their runout path, and as they come to rest. These forces generate seismic waves that can be used to estimate

the characteristics of the motion of a landslide. We present an approach for simulating the motion of rapid,

flowing landslides that considers different ways for the material to transition from being at rest to flowing, and

different landslide material representations that affect how the simulated landslide moves once it is in motion.

We then compare the forces estimated from the model of landslide motion with the forces estimated from the

seismic data. Using simulations with simple, idealized terrain and real events with complex terrain, we show

how terrain and different assumptions in the model for landslide motion affect the force estimation. We provide

additional insight on how seismic data can aid in interpreting the way in which motion begins and how a

landslide moves.

MITCHELL ETAL.

Insights on Multistage Rock Avalanche Behavior From Runout

Modeling Constrained by Seismic Inversions

A. Mitchell1,2 , K. E. Allstadt3 , D. George3 , J. Aaron4, S. McDougall1 , J. Moore5 , and

B. Menounos6

1Department of Earth, Ocean and Atmsopheric Sciences, University of British Columbia, Vancouver, BC, Canada,

2Now at BGC Engineering Inc., Vancouver, BC, Canada, 3U. S. Geological Survey, Golden, CO, USA, 4Swiss Federal

Institute for Forest, Snow and Landscape Research, Birmensdorf, Switzerland, 5Department of Geology & Geophysics,

University of Utah, Salt Lake City, UT, USA, 6Department of Earth and Environmental Science, University of Northern

British Columbia, Prince George, BC, Canada

Key Points:

• Different runout model material

representations and initial conditions

were tested to determine their

influence on seismic force estimates

• Real event simulations confirmed

the interplay between material

representation, topography, multistage

failures, and modeled seismic forces

• The magnitude of the simulated peak

forces was most sensitive to failures

separated by tens of seconds

Supporting Information:

Supporting Information may be found in

the online version of this article.

Correspondence to:

A. Mitchell,

AMitchell@bgcengineering.ca

Citation:

Mitchell, A., Allstadt, K. E., George,

D., Aaron, J., McDougall, S., Moore,

J., & Menounos, B. (2022). Insights

on multistage rock avalanche behavior

from runout modeling constrained

by seismic inversions. Journal of

Geophysical Research: Solid Earth,

127, e2021JB023444. https://doi.

org/10.1029/2021JB023444

Received 16 OCT 2021

Accepted 19 SEP 2022

Author Contributions:

Conceptualization: A. Mitchell, K. E.

Allstadt, D. George, S. McDougall

Formal analysis: A. Mitchell, K. E.

Allstadt, D. George, J. Aaron

Investigation: A. Mitchell

Methodology: A. Mitchell, K. E.

Allstadt, D. George, J. Aaron, S.

McDougall

Resources: J. Aaron, S. McDougall, J.

Moore, B. Menounos

Software: A. Mitchell, K. E. Allstadt

Visualization: A. Mitchell

Writing – original draft: A. Mitchell

Writing – review & editing: K.

E. Allstadt, D. George, J. Aaron, S.

McDougall, J. Moore, B. Menounos

10.1029/2021JB023444

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