Streamflow response in small upland catchments in the Chilean coastal range to the M_W 8.8 Maule earthquake on 27 February 2010

Abstract

[1] Hydrological response to earthquakes has long been observed, yet the mechanisms responsible still remain unclear and likely vary in space and time. This study explores the base flow response in small upland catchments of the Coastal Range of south-central Chile after the M W 8.8 Maule earthquake of 27 February 2010. An initial decline in streamflow followed by an increase of up to 400% of the discharge measured immediately before the earthquake occurred, and diurnal streamflow oscillations intensified after the earthquake. Neither response time, nor time to maximum streamflow discharge showed any relationship with catchment topography or size, suggesting non-uniform release of water across the catchments. The fast response, unaffected stream water temperatures and a simple diffusion model point to the sandy saprolite as the source of the excess water. Base flow recession analysis reveals no evidence for substantial enhancement of lateral hydraulic conductivity in the saprolite after the earthquake. Seismic energy density reached $170 J/m 3 for the main shock and $0.9 J/m 3 for the aftershock, exceeding the threshold for liquefaction by undrained consolidation only during the main shock. Although increased hydraulic gradient due to ground acceleration-triggered, undrained consolidation is consistent with empirical magnitude-distance relationships for liquefaction, the lack of independent evidence for liquefaction means that enhanced vertical permeability (probably in combination with co-seismic near-surface dilatancy) cannot be excluded as a potential mechanism. Undrained consolidation may have released additional water from the saturated saprolite into the overlying soil, temporarily reducing water transfer to the creeks but enlarging the cross-section of the saturated zone, which in turn enhanced streamflow after establishment of a new hydraulic equilibrium. The enlarged saturated zone facilitated water uptake by roots and intensified evapotranspiration.

Earthquake Hydrology

“…Mohr et al (2012) found that evapotranspiration and discharge both increased in small Chilean catchments after the M8.8 2010 Maule earthquake, suggesting that water drained from the unsaturated zone to the water table. Mohr et al (2012) found that evapotranspiration and discharge both increased in small Chilean catchments after the M8.8 2010 Maule earthquake, suggesting that water drained from the unsaturated zone to the water table.…”

“…Explanations for changes in streamflow can be divided into six categories: expulsion of deep crustal fluids resulting from coseismic elastic strain (e.g., Muir-Wood and King, 1993), changes in near-surface permeability (Briggs, 1991 and Wolf, 1992;Rojstaczer et al, 1995;Sato et al, 2000;Tokunaga, 1999), consolidation or even liquefaction of nearsurface deposits (Manga, 2001;Manga et al, 2003;, release of water from the unsaturated zone (Manga and Rowland, 2009;Mohr et al, 2012), rupturing of subsurface reservoirs (Wang et al, 2004c), and the release of water trapped in fault zones. The differences between these different explanations are nontrivial because of their implications for the magnitude of crustal permeability, its evolution, and the nature of groundwater flow paths.…”

Tidal response variation and recovery following the Wenchuan earthquake from water level data of multiple wells in the nearfield

“…; T.-P. Liu et al, 1989;Niwa et al, 2012;Roeloffs, 1996;Sil, 2006), springs and stream discharge (Manga, 2001;Manga and Rowland, 2009;Manga et al, 2003;Mohr et al, 2012;Montgomery and Manga, 2003;Wang et al, 2004). Among them, changes in well water levels are the most commonly reported phenomenon.…”

Streamflow Changes in the Vicinity of Seismogenic Fault After the 1999 Chi–Chi Earthquake

“…Generally, changes in groundwater level occur coseismically (Waller 1966;Roeloffs 1998;King and Igarashi 1999;Chia et al 2001;Cox et al 2012;Weingarten andGe 2014, He et al 2017), while changes in streamflow or spring flow appear after major earthquakes (Rojstaczer and Wolf 1992;MuirWood and King 1993;King et al 1994;Manga 2001;Manga et al 2003;Wang et al 2004a, b;Manga and Rowland 2009;Mohr et al 2012Mohr et al , 2017.…”

“…Significant streamflow increases were found to accompany major normal fault earthquakes, while small decreases were associated with reverse fault earthquakes. Soil liquefaction has been proposed for the streamflow increase (Manga 2001;Wang et al 2001;, but possibly limited to shallow sediments in the river valley of the mountain area (Mohr et al 2012).…”