Hidden Holocene slip along the coastal El Yolki fault in Central Chile and its possible link with megathrust earthquakes

Melnick, Daniel; Hillemann, Christian; Jara-Muñoz, Julius; Garrett, Ed; Cortés-Aranda, Joaquín; Molina, Diego; Tassara, Andrés; Strecker, Manfred R.

Abstract

Megathrust earthquakes are commonly accompanied by increased upper‐plate seismicity and occasionally triggered fault slip. In Chile, crustal faults slipped during and after the 2010 Maule (M8.8) earthquake. We studied the El Yolki fault (EYOF), a transtensional structure midways the Maule rupture not triggered in 2010. We mapped a Holocene coastal plain using LiDAR, which did not reveal surface ruptures. However, the inner‐edge and shoreline angles along the coastal plain as well as 4.3‐4.0 ka intertidal sediments are back‐tilted on the EYOF footwall block, documenting 10 m of vertical displacement. These deformed markers imply ~2 mm/yr throw rate and dislocation models a slip rate of 5.6 mm/yr for the EYOF. In a 5‐m‐deep trench, the Holocene intertidal sediments onlap to five erosive steps, interpreted as staircase wave‐cut landforms formed by discrete events of relative sea‐level drop. We tentatively associated these steps with coseismic uplift during EYOF earthquakes between 4.3 and 4.0 ka. The Maule earthquake rupture may be subdivided into three subsegments based on coseismic slip and gravity anomalies. Coulomb stress transfer models predict neutral stress changes at the EYOF during the Maule earthquake but positive changes for a synthetic slip distribution at the central subsegment. If EYOF earthquakes were triggered by megathrust events, their slip distribution was probably focused in the central subsegment. Our study highlights the millennial variability of crustal faulting and the megathrust earthquake cycle in Chile, with global implications for assessing the hazards posed by hidden but potentially seismogenic coastal faults along subduction zones.

Citation

Melnick, D., Hillemann, C., Jara-Muñoz, J., Garrett, E., Cortés-Aranda, J., Molina, D., …Strecker, M. R. (2019). Hidden Holocene slip along the coastal El Yolki fault in Central Chile and its possible link with megathrust earthquakes. Journal of Geophysical Research. Solid Earth, 124(7), 7280-7302. https://doi.org/10.1029/2018jb017188

• Journal Article Type: Article
• Acceptance Date: Jun 13, 2019
• Online Publication Date: Jul 9, 2019
• Publication Date: Jul 31, 2019
• Deposit Date: Jun 25, 2019
• Publicly Available Date: Jan 9, 2020
• Journal: Journal of Geophysical Research. Solid Earth
• Print ISSN: 2169-9313
• Publisher: American Geophysical Union
• Peer Reviewed: Peer Reviewed
• Volume: 124
• Issue: 7
• Pages: 7280-7302
• DOI: https://doi.org/10.1029/2018jb017188