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A Spectral Perspective on Fault Geometry and Strike-Slip Rupture at Plate-Boundary Scales Along the Queen Charlotte Fault

Description: 

We compare scalograms of fault geometry and yield stress to M~7+ ruptures along the Queen Charlotte Fault (QCF). Fault geometry controls stress accumulation and release during earthquakes, implying that sizes, locations, and magnitude distributions of earthquakes should mirror the sizes, locations, and scaling of geometric irregularities on faults. Along the QCF, O(100)-km-scale irregularities in the scalograms mark the extents of all recorded M~7+ ruptures, suggesting that large-scale irregularities act as barriers to rupture. Converting the geometry scalograms to yield stress shows that ruptures nucleate where yield stress equals average values and terminate in high yield stress regions (i.e., barriers). At scales shorter than total rupture length, co-seismic slip is, conversely, highest where yield stress is highest, indicating that longer ruptures release stress accumulated at smaller-scale irregularities. This barrier-asperity model is consistent with other spectral measurements. The O(100)-km scale marks a break in scaling of irregularity height H to length L ratios: At ~35 to 55 km scales, QCF geometry follows a self-affine H∝L^ζ scaling with ζ≈0.6. At scales >90 km, ζ≈0.9. The fractal break separates QCF rupture sizes: Mw 7.5 to 7.9 events are >90 km long, where ζ≈0.9; Mw 6.8 to 7.0 events are ~35 to 55 km long, where ζ≈0.6. No ~55 to 90-km-long ruptures have been recorded on the QCF. Consistently, the ~55 to 90 km transitional band marks an abrupt increase in irregularity amplitude and high yield stress variation, features that impede rupture. A scaling break at O(100) km is also apparent in the magnitude-frequency distribution (MFD) of QCF earthquakes. Many more great (M > 7.5, L > 100 km) earthquakes have occurred than predicted by Gutenberg-Richter scaling, meaning stress is more readily accommodated by large rather than small ruptures, consistent with predictions from the scalograms. The similar characteristic scaling in fault geometry and rupture distributions may arise from fundamental scale of strike-slip faulting, such as seismogenic zone depth.

Session: Structure, Seismicity and Dynamics of the Queen Charlotte-Fairweather Fault System - I

Type: Oral

Date: 5/1/2024

Presentation Time: 05:30 PM (local time)

Presenting Author: Nathaniel

Student Presenter: No

Invited Presentation: 

Authors