The implications of fault zone transformation on aseismic creep: Example of the North Anatolian Fault, Turkey

Abstract

Aseismic creep is observed at surface along several segments of the North Anatolian right‐lateral active fault in Turkey, a major plate boundary between Eurasia and Anatolia. Identifying the mechanisms that control creep and their temporal and spatial change represents a major challenge for predicting the mechanical evolution of active faults, the interplay between creep and earthquakes, and the link between short‐term observations from geodesy and the long‐term fault zone evolution. We combine geological observations, laboratory analyses, and imaging techniques, shedding new light on the mechanism of fault creep along the North Anatolian Fault (NAF) and its time‐dependent change. A clear correlation is shown between shallow creep and near‐surface fault gouge composition: locked segments of the NAF are mostly composed of massive limestones without clay gouges, whereas creeping segments comprise clay gouges that contain low‐friction minerals. Such fault gouges appear to result from a progressive change of initial volcanic host rocks during their deformation. Anastomosing cleavage develops during the first stage of displacement, leading to layering, oblique at first and then subparallel to the fault, which accommodates part of the aseismic creep by pressure solution. Soluble minerals are dissolved, leading to passive concentration of phyllosilicates in the gouges where alteration transformations by fluid flow produce low friction minerals. At the same time damage zones are fractured and fractures are sealed by carbonates. As a result, these mineralogical and structural transformations weaken the gouge and strengthen the damage zone leading to the change from diffuse to localized seismic‐aseismic zones.

Shallow Creep Along the 1999 Izmit Earthquake Rupture (Turkey) From GPS and High Temporal Resolution Interferometric Synthetic Aperture Radar Data (2011–2017)

“…However, geological maps reveal that the central section of the 1999 Izmit rupture coinciding with the maximum surface creep puts in contact Quaternary alluvial deposits in the central depression of the Izmit basin, north of the fault, and Eocene volcanic units south of the fault (Figure c). The weathering of these lenses of volcanic rocks could produce weak minerals such as saponite, favoring the persistency of high creep rate in this location (Kaduri et al, ). These volcanic units become thinner to the east of Sapanca Lake, which could explain why creep is vanishing eastward.…”

“…Based on the observations of the slow displacement of a wall at the train station of Ismetpasa in the period 1957-1969, and railway maintenance reports, the fault creeping behavior at Ismetpasa was first documented by Ambraseys (1970), a decade after the first observation of this phenomenon on the San Andreas Fault (Steinbrugge et al, 1960). Various measurements afterward (Global Positioning System [GPS], InSAR, light detection and ranging [LIDAR], creepmeter, and field observations) allowed to better characterize the spatiotemporal properties of creep along the Ismetpasa fault section (Aytun, 1982;Bilham et al, 2016;Cakir et al, 2005;Cetin et al, 2014;Deniz et al, 1993;Eren, 1984;Kaduri et al, 2017;Kaneko et al, 2013;Ozener et al, 2012;Rousset et al, 2016). All studies combined show that the creep rate is decaying with time following the 1944 rupture (Cetin et al, 2014), so that creep has been interpreted as postseismic relaxation.…”

“…All studies combined show that the creep rate is decaying with time following the 1944 rupture (Cetin et al, 2014), so that creep has been interpreted as postseismic relaxation. Gouges formed within the fault zone rocks contain low friction minerals that could explain the creeping behavior of the fault (Kaduri et al, 2017). long segment of the North Anatolian Fault Konca et al, 2010).…”

Fault Creep and Strain Partitioning in Trinidad‐Tobago: Geodetic Measurements, Models, and Origin of Creep

“…Creep in the San Andreas Fault system occurs on fault segments that contact the Coast Range ophiolite, where alteration to serpentine and other weak mineral phases or abnormally high fluid pore pressures occur (Irwin & Barnes, 1975;Melchiorre et al, 1999;Moore & Rymer, 2007;Sieh & Williams, 1990). Weak clay and mica, generated, concentrated, and oriented (foliated) in fault cores, can also facilitate aseismic creep (Kaduri et al, 2017, Schleicher et al, 2010. Particularly weak mineral phases include talc and saponite, which form from ophiolite alteration (Moore & Rymer, 2007;Richard et al, 2014).…”

“…Clay-rich fault gouge can reduce fault core permeability, trap fluids, create overpressure, and weaken rock (Blanpied et al, 1992;Faulkner & Rutter, 2001). Fluid can also move through a fault core and assist diffusive mass transfer (i.e., pressure solution), encouraging creep (Gratier et al, 2011, Kaduri et al, 2017.…”