Extension at the coast of the Makran subduction zone (Iran)

Abstract

In the Makran subduction zone, earthquake focal mechanisms and geodetic data indicate that the deforming prism currently experiences N-S compression. However, palaeostress inversions performed on normal faults observed along the coast reveal local stress components consistent with N-S extension. Previously proposed mechanisms such as gravitational collapse are not favoured by N-S compression and surface uplift. We propose that the observed kinematics result from transient stress reversals following large earthquakes. During the interseismic period (now), the region experiences N-S compression. However, following a large reverse rupture on the subduction interface, stresses in the inner wedge relax, enabling a brief period of extensional faulting before a compressive stress state is re-established. This mechanism, also observed in other subduction zones, requires low overall stresses in the upper plate and that the margin ruptures in large megathrust earthquakes that result in nearly complete stress drops. S U PP O RTI N G I N FO R M ATI O NAdditional supporting information may be found online in the Supporting Information section at the end of the article. Data S1. Fault inversion method.

Overriding Plate Deformation and Topography During Slab Rollback and Slab Rollover: Insights From Subduction Experiments

“…In nature, there is also a domain, the coastal Makran region at ∼120 and 180 km north of the trench, that is dominated by normal faults and extension. This extensional zone, however, likely does not correspond to the extensional domain found in our rollover experiments, as it is located above the subduction zone plate boundary interface in nature (Normand et al, 2019;Pajang et al, 2021) but above the sublithospheric mantle in our experiments. A possible explanation for the lack of an extensional zone further northward in the Makran domain is the much larger overriding plate (Eurasia), and thus larger resistance to motion, in nature, which would enhance horizontal trench-normal compressive stresses during slab rollover, thereby suppressing the local zone of extension.…”

Pleistocene Coastal Evolution in the Makran Subduction Zone

“…However, most sediments on the modern coast are reworked from emerged portions of the accretionary prism residing to the north of the studied area (McCall and Kidd, 1982;Ellouz-Zimmermann et al, 2007;Bourget et al, 2010). Data from offshore sedimentary structures and cores (Uchupi et al, 2002;Bourget et al, 2010), as well as the presence of extensive and fast-prograding Holocene beach ridges successions along the Makran coast (e.g., Shah-Hosseini et al, 2018;Normand et al, 2019b) evidence a high sedimentary input into the Oman Sea.…”

“…These Tertiary sedimentary units are faulted and deformed into wide, gently double-plunging, E-W trending anticlines and synclines, visible in satellite imagery (Figure 2; Farhoudi and Karig, 1977;Leggett and Platt, 1984;Samadian et al, 1994Samadian et al, , 1996Samadian et al, , 2004. Although reverse faulting is associated with the growth of folds both in the immerged part of the prism (offshore) and north of the coastal region (White and Louden, 1982;Grando and McClay, 2007), normal faults predominate close to the coastline (Ghorashi, 1978;Harms et al, 1984;Platt and Leggett, 1986;Snead, 1993;Dolati and Burg, 2013;Normand et al, 2019b).…”