Experimental evidence for seismically initiated gas bubble nucleation and growth in groundwater as a mechanism for coseismic borehole water level rise and remotely triggered seismicity

Abstract

Changes in borehole water levels and remotely triggered seismicity occur in response to near and distant earthquakes at locations around the globe, but the mechanisms for these phenomena are not well understood. Experiments were conducted to show that seismically initiated gas bubble growth in groundwater can trigger a sustained increase in pore fluid pressure consistent in magnitude with observed coseismic borehole water level rise, constituting a physically plausible mechanism for remote triggering of secondary earthquakes through the reduction of effective stress in critically loaded geologic faults. A portion of the CO 2 degassing from the Earth's crust dissolves in groundwater where seismic Rayleigh and P waves cause dilational strain, which can reduce pore fluid pressure to or below the bubble pressure, triggering CO 2 gas bubble growth in the saturated zone, indicated by a spontaneous buildup of pore fluid pressure. Excess pore fluid pressure was measured in response to the application of 0.1-1.0 MPa, 0.01-0.30 Hz confining stress oscillations to a Berea sandstone core flooded with initially subsaturated aqueous CO 2 , under conditions representative of a confined aquifer. Confining stress oscillations equivalent to the dynamic stress of the 28 June 1992 M w 7.3 Landers, California, earthquake Rayleigh wave as it traveled through the Long Valley caldera, and Parkfield, California, increased the pore fluid pressure in the Berea core by an average of 36 ± 15 cm and 23 ± 15 cm of equivalent freshwater head, respectively, in agreement with 41.8 cm and 34 cm rises recorded in wells at those locations.1. Background Coseismic Borehole Water Level RiseWater levels in some wells respond to near and distant earthquakes [Roeloffs et al., 1995Roeloffs, 1998;Woodcock and Roeloffs, 1996;Liu et al., 1989;Zones, 1957;Leggette and Taylor, 1934;Sterns, 1928]. The water level can increase or decrease in response to a change in static stress, but the coseismic water level changes in a subset of wells always have the same sign, regardless of the sign of the local static stress change. In wells that exhibit coseismic water level rise, the increase in water level scales with the earthquake magnitude, and inversely as the square of the distance to the hypocenter [Roeloffs, 1998]. Coseismic water level rise typically begins within minutes of the passage of the seismic surface wave train and builds to a peak over hours to days then slowly declines to or near pre-earthquake level within hours to weeks. The largest coseismic water level rise in a given well tends to occur when the pre-earthquake water level is at or near a seasonal low [Roeloffs, 1998]. The 28 June 1992 M w 7.3 Landers, California, earthquake induced water level changes ranging from À180 cm to +300 cm in wells in Parkfield, Long Valley caldera, and Southern California (Figure 1), and caused borehole water level oscillations in Oregon and Nevada [Roeloffs et al., 1995].The Bourdieu Valley well, 435 km from the Landers hypocenter, responded with a 34 cm incre...

Triggering of the largest Deccan eruptions by the Chicxulub impact

“…Indeed, permeability changes induced by earthquakes have been measured or inferred at depths up to many kilometers (e.g., Wang et al, 2013). It has also been documented experimentally that the temporary lowering of pressure during the passage of P and Rayleigh waves can nucleate CO 2 bubbles, leading to a net increase in pore pressure after the fi nal passage of the waves (Crews and Cooper, 2014).…”

Mechanism of co-seismic water level change following four great earthquakes – insights from co-seismic responses throughout the Chinese mainland

“…(2) Co-seismic bubble growth: passing seismic waves may nucleate gas bubbles or cause pre-existing bubbles to grow, increasing pore pressure because of volume expansion (Crews and Cooper, 2014;Linde et al, 1994;Matsumoto and Roeloffs, 2003). This mechanism requires that the groundwater contains or can nucleate gas bubbles such as CO 2 and also predicts that water levels should always rise.…”

“…These include: (1) poroelastic response to coseismic static strain (Ge and Stover, 2000;Jónsson et al, 2003;Shi et al, 2013b); (2) undrained consolidation of sediments (Wang and Chia, 2008); (3) clogging or unclogging pore and fractures by oscillatory flows produced by passing seismic waves Elkhoury et al, 2006;Lai et al, 2014;; (4) co-seismic gas bubble nucleation and growth (Crews and Cooper, 2014;Linde et al, 1994); (5) shaking-induced compaction or dilatation (Bower and Heaton, 1978;Zhang et al, 2015).…”

Sustained water‐level changes caused by damage and compaction induced by teleseismic earthquakes

“…Most of the macroscopic observations related to distant earthquakes are hydrological and relate to permeability enhancement [ Manga et al ., ; Xue et al ., ]. Seismic waves are known to cause oscillations in well water levels and in some occasions also to cause sustained water‐level changes [ Ben‐Zion et al ., ; Brodsky et al ., ; Crews and Cooper , ; Doan and Cornet , ; Manga et al ., ; Roeloffs et al ., ; Roeloffs , ; Shi et al ., ; Shi et al ., ; Wang and Manga , ; Yan et al ., ; Zhang et al ., ]. These observations and models account for sustained changes of the water level occurring during different periods.…”

“…Different mechanisms for coseismic well water‐level changes have been discussed. Among them are the intrusion of hot groundwater [ Roeloffs et al ., ], unclogging of the colloidal filling of fractures [ Brodsky et al ., ], mobilization of pore‐clogging gas bubbles [ Roeloffs , ], and gas bubble nucleation and growth [ Crews and Cooper , ].…”