Exploring patterns in seismic attenuation on rocky coasts to assess the potential for active rock damage processes and erosion
Abstract
The integration of wave energy by sea cliffs and its conversion into mechanical work and erosion represents a fundamental question in rocky coast geomorphology. The quantification of cliff response to waves can (1) refine predictions of cliff collapse and (2) strengthen the link to energy-based models for rocky coast evolution. A promising method for characterization of this coupling is via the use of networks of cliff-top seismometers, which provide high-resolution records of both environmental conditions and landscape response. We compare 5 cliff-top seismic records (Orkney Islands, UK; La Jolla, CA, USA; Santa Cruz, CA, USA; Boulby Cliffs, UK; and Okakari Point, NZ) to characterize the response of sea cliffs to wave action. Across all sites, ground displacement scales with wave magnitude and decays with distance from the cliff face. Using buoy and bathymetric data to constrain the location of wave breaking reveals that 4 of 5 sites behave in a mechanically consistent manner. Following this correction for breaking, decay in displacement at 4 sites is consistent with energy loss due entirely to geometric spreading of seismic waves. In contrast, the decay in ground displacement at Orkney is more pronounced, and is not explained by geometric spreading alone. We interpret this additional energy loss as a signature of damage accumulation. The degree of decay at Orkney increases with wave magnitude, suggesting that energy is more efficiently lost to crack growth during more intense wave forcing. We attribute the apparent importance of rock damage at Orkney to the concentration of breaking waves at the cliff face relative to other sites. This concentration of the breaking zone likely reduces energy dissipation prior to wave impact, allowing damage to more effectively accumulate. Given these differences between sites, our results suggest that, in some cases, rock damage processes can play an important role in driving rocky coast evolution. In this contribution, we will discuss the causes and consequences of these site differences and the role of rock damage with specific focus on near-shore processes and rocky coast evolution.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.S23B..01M