Fault segmentation: New concepts from the Wasatch Fault Zone, Utah, USA

Abstract

The question of whether structural segment boundaries along multisegment normal faults such as the Wasatch fault zone (WFZ) act as persistent barriers to rupture is critical to seismic hazard analyses. We synthesized late Holocene paleoseismic data from 20 trench sites along the central WFZ to evaluate earthquake rupture length and fault segmentation. For the youngest (<3 ka) and best‐constrained earthquakes, differences in earthquake timing across prominent primary segment boundaries, especially for the most recent earthquakes on the north‐central WFZ, are consistent with segment‐controlled ruptures. However, broadly constrained earthquake times, dissimilar event times along the segments, the presence of smaller‐scale (subsegment) boundaries, and areas of complex faulting permit partial‐segment and multisegment (e.g., spillover) ruptures that are shorter (~20–40 km) or longer (~60–100 km) than the primary segment lengths (35–59 km). We report a segmented WFZ model that includes 24 earthquakes since ~7 ka and yields mean estimates of recurrence (1.1–1.3 kyr) and vertical slip rate (1.3–2.0 mm/yr) for the segments. However, additional rupture scenarios that include segment boundary spatial uncertainties, floating earthquakes, and multisegment ruptures are necessary to fully address epistemic uncertainties in rupture length. We compare the central WFZ to paleoseismic and historical surface ruptures in the Basin and Range Province and central Italian Apennines and conclude that displacement profiles have limited value for assessing the persistence of segment boundaries but can aid in interpreting prehistoric spillover ruptures. Our comparison also suggests that the probabilities of shorter and longer ruptures on the WFZ need to be investigated.

Rupture Kinematics and Structural‐Rheological Control of the 2016 Mw6.1 Amatrice (Central Italy) Earthquake From Joint Inversion of Seismic and Geodetic Data

“…Cross structures may act as barriers to rupture and limit earthquake length (Benedetti et al, 2013;Manighetti et al, 2015), with critical consequences to seismic hazard assessment (DuRoss et al, 2016).…”

Fault Segmentation as Constraint to the Occurrence of the Main Shocks of the 2016 Central Italy Seismic Sequence

“…Tectonics, 36, 2370-2387. https://doi. org/10.1002/2017TC004652 systems until a continuous throughgoing major structure forms (e.g., DuRoss et al, 2016;Manighetti et al, 2015;Peacock et al, 2017;Scholz & Gupta, 2000)?…”

“…This issue is also closely linked to another debated relevant question: could a large structural barrier, separating two approaching fault systems, remain persistent through time, at most only occasionally breaking during its history for particular conditions of dynamic stress and strain accumulation (e.g., King & Nabelek, ; Schwartz, ; Schwartz & Coppersmith, ; Wesnousky, )? Or the barrier will eventually be bypassed by a newly formed fault that allows the progressive hard‐linkage of the two approaching fault systems until a continuous throughgoing major structure forms (e.g., DuRoss et al, ; Manighetti et al, ; Peacock et al, ; Scholz & Gupta, )?…”

Surface Faulting of the 30 October 2016 Mw 6.5 Central Italy Earthquake: Detailed Analysis of a Complex Coseismic Rupture

“…A critical step in seismic hazard assessments is the recognition of structural and geometric complexities within fault systems that hamper rupture propagation (barriers) or, conversely, may favor interaction of adjacent faults on different timescales (D'Alessio & Martel, ; Manighetti et al, ; Sibson, ; Wibberley et al, ). Ultimately, such knowledge yields the basis for establishing the segmented and interacting framework of seismogenic fault systems, with the chance to identify possible recurrent styles of coseismic faulting, potential rupture length, and organization (e.g., DuRoss et al, ; Machette et al, ). Therefore, the detailed analysis of coseismic surface ruptures may provide precious hints on active faults segmentation and the way they accumulate displacement and grow through time (Lin, ).…”