Seismic and aseismic slip evolution and deformation associated with the 2009-2010 northern Malawi earthquake swarm, East African Rift

Abstract

SUMMARY Interferometric synthetic aperture radar (InSAR) measurements, field observations and elastic modelling of the 2009–2010 Karonga (northern Malawi) earthquake swarm reveal widespread coseismic and localized post‐seismic deformation. In a period of about 1.5 months starting on November 5, 29 M ≥ 4 earthquakes struck the region, culminating in an Mw 6 peak event on December 19. The next few months were characterized by significant localized deformation with a very low seismic moment release. We find a very good agreement between InSAR and field observations of surface ruptures. Our best fitted coseismic models indicate dip‐slip displacements on a fault dipping 40° to the southwest with maximum slip of about 120 cm at 3–5 km depth. Fault activity continued until 2010 August as shallow aseismic afterslip mostly above the maximum coseismic slip patches. Although the swarm occurred within a coastal plain covered by porous Quaternary sediments and a high water table, the effect of poroelastic relaxation on the post‐seismic deformation was found to be negligibly small. In contrast with other recent earthquake swarms along the East African Rift, the Karonga swarm shows no evidence for dike intrusion.

Active Deformation of Malawi Rift's North Basin Hinge Zone Modulated by Reactivation of Preexisting Precambrian Shear Zone Fabric

“…The series of earthquakes damaged thousands of houses and resulted in several fatalities (Biggs et al, ). Additional series of M b ≤ 4.6 earthquakes were recorded until one month after the larger events (Hamiel et al, ). The M w ≥ 4.9 earthquakes, occurring at <10 km focal depths, were accompanied by coseismic surface ruptures of 35–43 cm vertical displacements (Hamiel et al, ; Macheyeki et al, ) and liquefaction‐related sand blows within the surficial coastal plain sediments.…”

“…Additional series of M b ≤ 4.6 earthquakes were recorded until one month after the larger events (Hamiel et al, ). The M w ≥ 4.9 earthquakes, occurring at <10 km focal depths, were accompanied by coseismic surface ruptures of 35–43 cm vertical displacements (Hamiel et al, ; Macheyeki et al, ) and liquefaction‐related sand blows within the surficial coastal plain sediments. Differential interferometric synthetic aperture radar (DInSAR) modeling of the surface deformation associated with the coseismic events suggests that the earthquakes were not associated with magmatic emplacement (Biggs et al, ).…”

“…Differential interferometric synthetic aperture radar (DInSAR) modeling of the surface deformation associated with the coseismic events suggests that the earthquakes were not associated with magmatic emplacement (Biggs et al, ). Instead, these studies found that the earthquake sequence was associated with the rupture of a shallow single NNW‐SSE striking and SW dipping normal fault (Biggs et al, ; Hamiel et al, ; Macheyeki et al, ) associated with active deformation of the half‐graben hinge zone. Hamiel et al () documented a cumulative surface rupture length of 18 km, while Macheyeki et al () estimated a total rupture length of 14.3 km.…”

Coseismic and postseismic deformation due to the 2007 M5.5 Ghazaband fault earthquake, Balochistan, Pakistan

“…Space-geodetic observations of afterslip over the past two decades provide an opportunity to better understand the nature of afterslip. Afterslip generally surrounds the high-slip patches of the coseismic rupture [Marone et al, 1991;Perfettini and Avouac, 2007] and has been observed following strike-slip [Freed, 2007;Furuya and Satyabala, 2008;Hearn et al, 2009], thrust [Podgorski et al, 2007], and normal crustal earthquakes [Hamiel et al, 2012], following subduction earthquakes [Miyazaki et al, 2004;Hsu et al, 2006;Sun et al, 2014] and following a detachment fault earthquake [Owen and Bürgmann, 2006]. Figure 4 shows the ratio of the aseismic moment release by afterslip relative to the coseismic moment release for 22 earthquakes in different tectonic settings (references are in Table S1).…”

Acquisition of a Unique Onshore/Offshore Geophysical and Geochemical Dataset in the Northern Malawi (Nyasa) Rift

“…InSAR data are collected over the region infrequently by most satellites, and some satellites have made no useful observations. But sufficient data from several satellites exist to observe ground deformation-principally from the European Space Agency's Envisat and Sentinal-1 satellites and the Japanese Space Agency's ALOS-1 satellite (Biggs et al, 2010;Hamiel et al, 2012). The GPS network includes 12 continuous GPS stations deployed in Malawi, Tanzania, and Zambia (Fig.…”