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Active thrust sheet deformation over multiple rupture cycles; a quantitative basis for relating terrace folds to fault slip rates

Joseph M. Stockmeyer, John H. Shaw, Nathan D. Brown, Edward J. Rhodes, Paul W. Richardson, Maomao Wang, Leore C. Lavin and Shuwei Guan
Active thrust sheet deformation over multiple rupture cycles; a quantitative basis for relating terrace folds to fault slip rates
Geological Society of America Bulletin (May 2017) 129 (9-10): 1337-1356

Abstract

Many recent thrust fault earthquakes have involved coseismic surface faulting and surface folding strains. This multifaceted nature of active thrust sheet deformation can make attempts to quantify slip and slip rates from surface strains challenging and uncertain. We present new methods for integrating records of surface deformation, subsurface structure, and geochronology to investigate active deformation over multiple rupture cycles across the Southern Junggar Thrust in the southern Junggar Basin, NW China, from approximately 225 ka to present. Fluvial terraces preserve records of surface faulting as a prominent fault scarp where the Southern Junggar Thrust is surface-emergent. Terraces also exhibit progressive folding strains across fold scarps that are spatially coincident with subsurface fault-bend folds-constrained by seismic reflection data-along the Southern Junggar Thrust. We quantify the fault slip at depth implied by fold scarp relief along Holocene-aged terraces, and the results are corroborated by independent estimates of slip implied by fault scarp relief for the same terraces. Older terraces exhibit a distinct fanning of dips across fold scarps, suggesting active fault-bend folding kinematics involving a component of limb rotation. We developed quantitative relations for fault-bend folds between fault slip and fold dip using a mechanical, forward modeling approach. Using this novel method, we show how Southern Junggar Thrust slip rate has decelerated markedly, from approximately 4.1 mm/yr in the middle Quaternary to approximately 1.2 mm/yr throughout the Holocene. These results provide new insight into natural fault-bend folding kinematics and define innovative methods for elucidating accurate estimates of fault slip and slip rates from terrace folds in active thrust sheets.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 129
Serial Issue: 9-10
Title: Active thrust sheet deformation over multiple rupture cycles; a quantitative basis for relating terrace folds to fault slip rates
Affiliation: Harvard University, Department of Earth and Planetary Sciences, Cambridge, MA, United States
Pages: 1337-1356
Published: 20170522
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 10
Accession Number: 2017-075983
Categories: Structural geologySeismology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2017147
Illustration Description: illus. incl. 4 tables, geol. sketch maps
N44°10'00" - N46°19'60", E85°00'00" - E91°00'00"
Secondary Affiliation: University of California at Los Angeles, USA, United StatesUniversity of Oregon, USA, United StatesPetroChina, CHN, China
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201740
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