Evidence for cross rift structural controls on deformation and seismicity at a continental rift caldera

Ryan Lloyd*, Juliet Biggs, Matthew Wilks, Andy Nowacki, J. Michael Kendall, Atalay Ayele, Elias Lewi, Hjálmar Eysteinsson

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)

17 Citations (Scopus)
288 Downloads (Pure)

Abstract

In continental rifts structural heterogeneities, such as pre-existing faults and foliations, are thought to influence shallow crustal processes, particularly the formation of rift faults, magma reservoirs and surface volcanism. We focus on the Corbetti caldera, in the southern central Main Ethiopian Rift. We measure the surface deformation between 22nd June 2007 and 25th March 2009 using ALOS and ENVISAT SAR interferograms and observe a semi-circular pattern of deformation bounded by a sharp linear feature cross-cutting the caldera, coincident with the caldera long axis. The signal reverses in sign but is not seasonal: from June to December 2007 the region south of this structure moves upwards 3 cm relative to the north, while from December 2007 until November 2008 it subsides by 2 cm. Comparison of data taken from two different satellite look directions show that the displacement is primarily vertical. We discuss potential mechanisms and conclude that this deformation is associated with pressure changes within a shallow (<1 km) fault-bounded hydrothermal reservoir prior to the onset of a phase of caldera-wide uplift.Analysis of the distribution of post-caldera vents and cones inside the caldera shows their locations are statistically consistent with this fault structure, indicating that the fault has also controlled the migration of magma from a reservoir to the surface over tens of thousands of years. Spatial patterns of seismicity are consistent with a cross-rift structure that extents outside the caldera and to a depth of ∼30 km, and patterns of seismic anisotropy suggests stress partitioning occurs across the structure. We discuss the possible nature of this structure, and conclude that it is most likely associated with the Goba-Bonga lineament, which cross-cuts and pre-dates the current rift. Our observations show that pre-rift structures play an important role in magma transport and shallow hydrothermal processes, and therefore they should not be neglected when discussing these processes.
Original languageEnglish
Pages (from-to)190-200
Number of pages11
JournalEarth and Planetary Science Letters
Volume487
Early online date13 Feb 2018
DOIs
Publication statusPublished - 1 Apr 2018

Keywords

  • rift volcanism
  • inherited structures
  • surface deformation
  • magma reservoirs
  • hydrothermal reservoirs

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