Relationship between earthquake swarm, rifting history, magmatism and pore pressure diffusion — an example from South Andaman Sea, India

Abstract

An extraordinarily strong and persistent earthquake swarm (Andaman swarm 2005) originated in the Andaman back-arc following the aftershock sequences of the 26 December 2004 Sumatra earthquake. The swarm (n = 651, mb max = 5.9) came mainly in two phases: January 26-31 and Feb. -Aug. 2005, in an area of size 90 x 40 km 2 , at the centre of which lies a broad bathymetric depression and high gravity zone. The swarm demonstrates a complex faulting series, initially the strike-slip motion followed by normal faulting in repetitive sequences, whose representative fault planes orient at high angle to the regional faults. The swarm character as well as the distribution of stress-axes and their correlation to tectonic features lends speculation for formation of a nascent rift segment in NW-SE direction at the doorstep of the Sewell Seamount. The swarm has given rise to 21 episodes of rifting activities of variable time extent within 26 -31 January 2005. The r-t plots corresponding to the swarm data, modelled with variable hydraulic diffusivity (D) values 4, 6, 8 and 10 m 2 /s, suggest for excess pressure front from ascending magmatic fluid. This eventually heralded the rifting; causing pore pressure perturbations that propagated in accordance with known diffusion parabolic equations.

Incipient status of dyke intrusion in top crust – evidences from the Al-Ays 2009 earthquake swarm, Harrat Lunayyir, SW Saudi Arabia

“…Furthermore, if we consult the ''Magma injection model'' of Hill's (Hill 1977) in rifted areas which commonly invokes the injection of shallow, vertical, en-echelon dykes extending along a narrow rift zone, this injection accounts initial strike slip motion along the fault planes followed by the collapse of closely spaced inner rift wall with earthquakes of normal fault source mechanism. The same is corroborated by other studies (Bergmann andSolomon 1990, Elsworth andVoigt 1995) including our own study in the South Andaman Sea (Mukhopadhyay et al 2010). In this Al Ays swarm sequence; we only have normal earthquakes (table 2).…”

“…The earthquake points in the r-t plot with modelled diffusivity value D of 0.1 m 2 /s lie below the modelled parabolic curve (figure 6), where, the swarm relates to the diffusion of pore pressure in a poro-elastic fluid saturated medium. The pore-pressure perturbations that generate earthquake swarm in divergent pull-apart basins are initiated by magmatic dyke intrusion from mantle source (also refer Mukhopadhyay et al 2010Mukhopadhyay et al , 2011. A very high pore pressure activity with low diffusivity along narrow zone of volcanic dyke intrusion with depths from 15 to 20 km can be inferred.…”

Seismic clusters and their characteristics at the Arabian Sea Triple Junction: Supportive evidences for plate margin deformations

“…The r-t plot for D values of 8 m 2 /s for earthquakes of 1975 swarm follows the parabolic equations (Fig.5), where, the swarm relates to the diffusion of pore pressure perturbations in a poro-elastic fluid saturated medium. The pore-pressure perturbations that generate earthquake swarm in divergent pull-apart basins are initiated by magmatic dyke intrusion from mantle source (also refer Mukhopadhyay et al 2010). Similar condition seemingly exists in this ridge segment.…”

“…It indicates a mechanism of repeated collapsing of rift wall by gravity faults during spreading, to generate seismicity along these ridge segments. We have suggested earlier a probable mechanism for the related process (Mukhopadhyay et al 2010). Basic features involved here are: crustal thinning, deformation on the top basement and sub-crustal mass anomalies, with exhumed mantle material (Leroy et al 2004).…”

Modelling the pore fluid diffusion process in aftershock initiation for 2004 Sumatra earthquake: implications for marine geohazard estimation in the Andaman region

“…The swarm demonstrates a complex faulting series: initially with strike-slip motion followed by normal faulting in periodic successions whose representative fault planes orient at high angle to the regional faults. The swarm character as well as the distribution of stress axes and their correlation with tectonic features lend speculation for formation/activation of a nascent rift in NW-SE direction at the doorstep of the Sewell Seamount (Mukhopadhyay et al 2010).…”