Uncertainty in strain-rate from field measurements of the geometry, rates and kinematics of active normal faults: Implications for seismic hazard assessment

Sgambato, Claudia; Walker, Joanna Faure; Roberts, Gerald

doi:10.1016/j.jsg.2019.103934

Cited by 15 publications

(16 citation statements)

References 84 publications

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“…The depth chosen for the brittle/viscous transition is consistent with hypocentral depths and coseismic slip in the Apennines 44 – 46 , and consistent with previous modelling 10 , 11 . The annual rate of slip is calculated using the Holocene throws measured at surface, using new data and data from previous works 10 , 14 , 18 , 19 , 25 – 27 . A triangular profile is assumed for the interseismic slip distribution, by linearly interpolating between the values of slip-rate measured at the surface, and thereafter decreased to zero at the tips.…”

Section: Methodsmentioning

confidence: 99%

“…1 c,d). Creep rates were assumed to be identical to slip-rates measured at the surface since 15 ± 3 ka 11 , with values from published sources and our own mapping 10 , 14 , 18 , 19 , 25 – 27 . Any postseismic afterslip on surface scarps would be included in surface slip values so the interseismic creep modelled includes postseismic afterslip, so we do not model postseismic stress changes due to viscoelastic afterslip separately 28 .…”

Section: Earthquake Deformation In the Southern Apennines And Model Smentioning

confidence: 99%

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Stress loading history of earthquake faults influenced by fault/shear zone geometry and Coulomb pre-stress

Sgambato

Walker

Mildon

et al. 2020

Sci Rep

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Whether the stress-loading of faults to failure in earthquakes appears to be random or to an extent explainable, given constraints on fault/shear-zone interaction and the build-up and release of stress over many earthquake cycles, is a key question for seismic hazard assessment. Here we investigate earthquake recurrence for a system of 25 active normal faults arranged predominantly along strike from each other, allowing us to isolate the effects of stress-loading due to regional strain versus across-and along-strike fault interaction. We calculate stress changes over 6 centuries due to interseismic loading and 25 > Mw 5.5 earthquakes. Where only one fault exists across strike, stressloading is dominated by the regional tectonics through slip on underlying shear zones and fault planes have spatially smooth stress with predominantly time-dependent stress increase. Conversely, where faults are stress-loaded by across-strike fault interactions, fault planes have more irregular stress patterns and interaction-influenced stress loading histories. Stress-loading to failure in earthquakes is not the same for all faults and is dependent on the geometry of the fault/shear-zone system. The stress-loading of faults to failure in earthquakes is driven by regional tectonics, but is also influenced by fault interaction during earthquakes, evidenced by calculations of Coulomb stress transfer (CST) and corresponding changes in the rate of seismicity 1-3. Faults also interact over longer time periods evidenced by fault displacement profiles that show steep displacement gradients and enhanced displacements on adjacent fault tips 4,5 , and observations of finite fault displacement profiles that adhere to global scaling relationships between fault length and fault displacement, both for isolated faults and for closely-spaced fault networks (d = γL, where γ = 0.03 for both isolated faults and summed across the strike of fault networks 6,7). However, despite the above evidence for organisation of both the stress-loading to failure process and long-term displacement accumulation, earthquake recurrence is often considered to be a random Poisson process for some seismic hazard purposes 8,9. The link between fault interaction during single earthquakes and over multiple seismic cycles described above argues that the recurrence of earthquakes must sum to produce the long-term displacement profiles. Hence displacement accumulation during earthquakes over the long-term is not random, and must be influenced by interaction, which is in turn governed by fault system geometry. However, study of geometry-controlled interaction is complicated by the fact that fault systems are complex, commonly exhibiting multiple overlapping faults, and it is difficult to isolate the effects of earthquake-inducing stress accumulation caused by tectonic loading as opposed to loading due to rupture of neighbouring faults both along and across strike 10. Without isolation of these effects it is challenging to assess what aspects of the stress-loading to failure, and h...

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Section: Methodsmentioning

confidence: 99%

Section: Earthquake Deformation In the Southern Apennines And Model Smentioning

confidence: 99%

Stress loading history of earthquake faults influenced by fault/shear zone geometry and Coulomb pre-stress

Sgambato

Walker

Mildon

et al. 2020

Sci Rep

Self Cite

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“…Thanks to the availability of Fault2SHA-CAD, we can propose a new generation of fault-based PSHA with codes that are capable of analyzing complex database structures, linking the variability in the available geological data to the variability in hazard and risk assessment. Accounting for slip rate variability along faults is paramount in fault-based PSHA in order to avoid underestimating (or overestimating) hazard as already pointed out by Faure Walker et al (2019) and Sgambato et al (2020) on single faults. Here, we went a step beyond by incorporating multi fault ruptures.…”

Section: Discussionmentioning

confidence: 99%

Which Fault Threatens Me Most? Bridging the Gap Between Geologic Data-Providers and Seismic Risk Practitioners

et al. 2021

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The aim of the Fault2SHA European Seismological Commission Working Group Central Apennines laboratory is to enhance the use of geological data in fault-based seismic hazard and risk assessment and to promote synergies between data providers (earthquake geologists), end-users and decision-makers. Here we use the Fault2SHA Central Apennines Database where geologic data are provided in the form of characterized fault traces, grouped into faults and main faults, with individual slip rate estimates. The proposed methodology first derives slip rate profiles for each main fault. Main faults are then divided into distinct sections of length comparable to the seismogenic depth to allow consideration of variable slip rates and the exploration of multi-fault ruptures in the computations. The methodology further allows exploration of epistemic uncertainties documented in the database (e.g., main fault definition, slip rates) as well as additional parameters required to characterize the seismogenic potential of fault sources (e.g., 3D fault geometries). To illustrate the power of the methodology, in this paper we consider only one branch of the uncertainties affecting each step of the computation procedure. The resulting hazard and typological risk maps allow both data providers and end-users 1) to visualize the faults that threaten specific localities the most, 2) to appreciate the density of observations used for the computation of slip rate profiles, and 3) interrogate the degree of confidence on the fault parameters documented in the database (activity and location certainty). Finally, closing the loop, the methodology highlights priorities for future geological investigations in terms of where improvements in the density of data within the database would lead to the greatest decreases in epistemic uncertainties in the hazard and risk calculations. Key to this new generation of fault-based seismic hazard and risk methodology are the user-friendly open source codes provided with this publication, documenting, step-by-step, the link between the geological database and the relative contribution of each section to seismic hazard and risk at specific localities.

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“…Iezzi et al, 2018). If fault bends are not recognised, this could lead to overestimates of palaeoearthquake magnitudes from palaeoseismological trenches (Sgambato et al, 2020).…”

Section: Discussionmentioning

confidence: 99%

Throw-rate variations within linkage zones during the growth of normal faults: Case studies from the Western Volcanic Zone, Iceland

Iezzi

Roberts

Walker

2020

Journal of Structural Geology

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This work investigates how throw-rates vary within fault bends and sites of fault linkage during the process of normal fault growth. In the Western Volcanic Zone, Iceland, through detailed field mapping and field measurements of fault throws, normal faults are mapped and along-strike throw profiles are constructed in order to understand how the throw-rates relate with the local fault geometry along faults at different stages of linkage. The results show that throw-rates increase within linkage zones and propagating fault bends independently from the stage of maturity of the fault bend. This implies that 1) the relationship between the local fault geometry and the along-strike distribution of throw-rate is driven by the deeper part of the fault, where established fault bends start propagating to the surface; 2) faults grow first by linkage and coalescence of separate faults, and then by accumulation of slip on the resultant fault, in agreement with models of fault growth by linkage and coalescence; 3) incipient fault bends can produce uncertainty associated with palaeoseismological results, if fault bends remain unrecognised. Moreover, this work demonstrates that existing models showing increased co-seismic and throw-rates within fault bends and sites of fault linkage found in continental extensional settings are valid in a geodynamic context of a mid-oceanic rifts.

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Uncertainty in strain-rate from field measurements of the geometry, rates and kinematics of active normal faults: Implications for seismic hazard assessment

Cited by 15 publications

References 84 publications

Stress loading history of earthquake faults influenced by fault/shear zone geometry and Coulomb pre-stress

Stress loading history of earthquake faults influenced by fault/shear zone geometry and Coulomb pre-stress

Which Fault Threatens Me Most? Bridging the Gap Between Geologic Data-Providers and Seismic Risk Practitioners

Throw-rate variations within linkage zones during the growth of normal faults: Case studies from the Western Volcanic Zone, Iceland

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