Evidence of seismic slip on a large splay fault in the Hikurangi subduction zone

<p>Observations from recent great subduction zone earthquakes highlight the influence of spatial geologic heterogeneity on overall rupture characteristics, such as areas of high co-seismic slip, and resulting tsunami generation.&#160; Defining the relevant spatial heterogeneity is thus important to understanding potential hazards associated with the megathrust. The more frequent, smaller magnitude earthquakes that commonly occur in subduction zones are often used to help delineate the spatial heterogeneity.&#160; Here we provide an overview of several subduction zones, including Costa Rica, Mexico, and Cascadia, highlighting connections between the small earthquake source characteristics and rupture behavior of larger earthquakes.&#160; Estimates of small earthquake locations and stress drop are presented in each location, utilizing data from coastal and/or ocean bottom seismic stations.&#160; These seismicity characteristics are then compared with other geologic and geophysical parameters, such as upper and lower plate characteristics, geodetic locking, and asperity locations from past large earthquakes. &#160;For example, in the Cascadia subduction zone, we find clusters of small earthquakes located in regions of previous seamount subduction, with variations in earthquake stress drop reflecting potentially disrupted upper plate material deformed as a seamount passed.&#160; Other variations in earthquake location and stress drop can be correlated with observed geodetic locking variations.&#160;</p>

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Frictional and hydrologic properties of a major splay fault system, Nankai subduction zone

Geophysical Research Letters ◽

10.1029/2009gl040009 ◽

2009 ◽

Vol 36 (20) ◽

Cited By ~ 42

Author(s):

Matt J. Ikari ◽

Demian M. Saffer ◽

Chris Marone

Keyword(s):

Subduction Zone ◽

Fault System ◽

Nankai Subduction Zone ◽

Splay Fault

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Fluid pressurisation and earthquake propagation in the Hikurangi subduction zone

10.5194/egusphere-egu21-8241 ◽

2021 ◽

Author(s):

Stefano Aretusini ◽

Francesca Meneghini ◽

Elena Spagnuolo ◽

Christopher Harbord ◽

Giulio Di Toro

Keyword(s):

Shear Strength ◽

Pore Pressure ◽

Subduction Zone ◽

Subduction Zones ◽

Fluid Pressure ◽

Low Permeability ◽

Earthquake Rupture ◽

Fault Rocks ◽

Seismic Slip ◽

Saturated Clay

<p>In subduction zones, seismic slip at shallow crustal depths can lead to the generation of tsunamis. Large slip displacements during tsunamogenic earthquakes are attributed to the low coseismic shear strength of the fluid-saturated and non-lithified clay-rich fault rocks. However, because of experimental challenges in confining these materials, the physical processes responsible of the coseismic reduction in fault shear strength are poorly understood. Using a novel experimental setup, we measured pore fluid pressure during simulated seismic slip in clay-rich materials sampled from the deep oceanic drilling of the P&#257;paku thrust (Hikurangi subduction zone, New Zealand). Here we show that seismic slip is characterized by an initial decrease followed by an increase of pore pressure. The initial pore pressure decrease is indicative of dilatant behavior. The following pore pressure increase, enhanced by the low permeability of the fault, reduces the energy required to propagate earthquake rupture. We suggest that thermal and mechanical pressurisation of fluids facilitates seismic slip in the Hikurangi subduction zone, which was tsunamigenic about 70 years ago. Fluid-saturated clay-rich sediments, occurring at shallow depth in subduction zones, can promote earthquake rupture propagation and slip because of their low permeability and tendency to pressurise when sheared at seismic slip velocities.</p>

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Seismic imaging of a megathrust splay fault in the North Chilean subduction zone (Central Andes)

Tectonophysics ◽

10.1016/j.tecto.2016.02.039 ◽

2016 ◽

Vol 689 ◽

pp. 157-166 ◽

Cited By ~ 3

Author(s):

Ina Storch ◽

Stefan Buske ◽

Cedric Schmelzbach ◽

Peter Wigger

Keyword(s):

Subduction Zone ◽

Seismic Imaging ◽

Central Andes ◽

The North ◽

Splay Fault

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Seismic images of the Northern Chilean subduction zone at 19°40′S, prior to the 2014 Iquique earthquake

Geophysical Journal International ◽

10.1093/gji/ggab035 ◽

2021 ◽

Vol 225 (2) ◽

pp. 1048-1061

Author(s):

Ina Storch ◽

Stefan Buske ◽

Pia Victor ◽

Onno Oncken

Keyword(s):

Subduction Zone ◽

Root Zone ◽

Accretionary Prism ◽

Depth Image ◽

Plate Interface ◽

Data Set ◽

Nazca Plate ◽

Depth Migration ◽

Splay Faults ◽

Splay Fault

SUMMARY The Northern Chilean subduction zone is characterized by long-term subduction erosion with very little sediment input at the trench and the lack of an accretionary prism. Here, multichannel seismic reflection (MCS) data were acquired as part of the CINCA (Crustal Investigations off- and onshore Nazca Plate/Central Andes) project in 1995. These lines cover among others the central part of the MW 8.1 Iquique earthquake rupture zone before the earthquake occurred on 1 April 2014. We have re-processed one of the lines crossing the updip parts of this earthquake at 19°40′S, close to its hypocentre. After careful data processing and data enhancement, we applied a coherency-based pre-stack depth migration algorithm, yielding a detailed depth image. The resulting depth image shows the subduction interface prior to the Iquique megathrust earthquake down to a depth of approximately 16 km and gives detailed insight into the characteristics of the seismogenic coupling zone. We found significantly varying interplate reflectivity along the plate interface which we interpret to be caused by the comparably strong reflectivity of subducted fluid-rich sediments within the grabens and half-grabens that are predominant in this area due to the subduction-related bending of the oceanic plate. No evidence was found for a subducted seamount associated to the Iquique Ridge along the slab interface at this latitude as interpreted earlier from the same data set. By comparing relocated fore- and aftershock seismicity of the Iquique earthquake with the resulting depth image, we can divide the continental wedge into two domains. First, a frontal unit beneath the lower slope with several eastward dipping back-rotated splay faults but no seismicity in the upper plate as well as along the plate interface. Secondly, a landward unit beneath the middle slope with differing reflectivity that shows significant seismicity in the upper plate as well as along the plate interface. Both units are separated by a large eastward dipping mega splay fault, the root zone of which shows diffuse seismicity, both in the upper plate and at the interface. The identification of a well-defined nearly aseismic frontal unit sheds new light on the interplate locking beneath the lower continental slope and its controls.

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Fluid pressurisation and earthquake propagation in the Hikurangi subduction zone

Nature Communications ◽

10.1038/s41467-021-22805-w ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

S. Aretusini ◽

F. Meneghini ◽

E. Spagnuolo ◽

C. W. Harbord ◽

G. Di Toro

Keyword(s):

Shear Strength ◽

Subduction Zone ◽

Subduction Zones ◽

Seismic Velocity ◽

Fluid Pressure ◽

Velocity Shear ◽

Low Permeability ◽

Earthquake Rupture ◽

Seismic Slip ◽

Saturated Clay

AbstractIn subduction zones, seismic slip at shallow crustal depths can lead to the generation of tsunamis. Large slip displacements during tsunamogenic earthquakes are attributed to the low coseismic shear strength of the fluid-saturated and non-lithified clay-rich fault rocks. However, because of experimental challenges in confining these materials, the physical processes responsible for the coseismic reduction in fault shear strength are poorly understood. Using a novel experimental setup, we measured pore fluid pressure during simulated seismic slip in clay-rich materials sampled from the deep oceanic drilling of the Pāpaku thrust (Hikurangi subduction zone, New Zealand). Here, we show that at seismic velocity, shear-induced dilatancy is followed by pressurisation of fluids. The thermal and mechanical pressurisation of fluids, enhanced by the low permeability of the fault, reduces the energy required to propagate earthquake rupture. We suggest that fluid-saturated clay-rich sediments, occurring at shallow depth in subduction zones, can promote earthquake rupture propagation and slip because of their low permeability and tendency to pressurise when sheared at seismic slip velocities.

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