The Role of Heterogeneity on Dynamic Weakening and Strengthening Mechanisms during Transport of the Mega-Scale Marysvale Gravity Slide Complex
Abstract
The Marysvale gravity slide complex of southwestern Utah, composed of the Sevier, Markagunt, and Black Mountain slides, ranks among the largest gravitational collapse structures on Earth, with an extent of > 8000 km2. In each event, the 2 to 3 km thick allochthonous plate translated more than 30 km over the former Oligocene to Miocene land surface, orders of magnitude larger than slip in during a typical fault rupture. Field evidence including clastic dikes, pseudotachylyte, extensive damage, hydrothermal alteration, and breccia development within a narrow basal shear zone and overlying slide mass support a high-velocity, catastrophic emplacement. Over this extensive runout distance, heterogeneity in the thermo-hydro-mechanical properties of the basal shear zone due to varying lithologies, pre-existing topography of the paleo-land surface and related asperities between the upper and lower plate, and an evolving damage state due to mechanical breakdown, wear, and deposition of the upper plate greatly impact the physical processes controlling slip. Here, we present field evidence and preliminary numerical model results of the shear zone processes along the Sevier and Markagunt gravity slides that governed slide transport during this single slip event. Based on laboratory measurements we find that permeability of the various rock units present vary by several of orders of magnitude in their intact state. Brittle damage accrued during slide motion is expected to induce even more variability. To evaluate how spatio-temporally varying heterogeneity along the length (>95 km) of the basal surface collectively drives slip acceleration and cessation during mega-scale catastrophic gravity slide emplacement, we idealize the landslide system in numerical models as a series of blocks connected by springs and simulate the coupled processes of frictional heating, fluid diffusion, and heat flow for multiple lithologies in simultaneous contact across the slide interface. Each block is assigned varying properties that can be tailored based on model inputs identified by field observation, detailed mapping, and laboratory measurements to represent heterogeneity during slip, and we discuss the net impact on dynamic weakening or strengthening of the slide interface.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFMMR35B..33B