Cascading Hazards in a Migrating Forearc-Arc System: Earthquake and Eruption Triggering in Nicaragua

Strain partitioning in oblique convergent margins results in margin-parallel shear in the overriding plate. Margin-parallel shear is often accommodated by margin-parallel strike-slip faults proximal to active volcanic arcs. Along the Nicaraguan segment of the Central American Forearc (CAFA) in the Cocos-Caribbean plate convergent margin, there are no well-expressed right-lateral faults that accommodate CA-CAFA relative motion. Instead, historical earthquakes and mapped fault orientations indicate that the ∼12 mm/yr of dextral motion is accommodated on arc-normal, left-lateral faults (i.e., bookshelf faults). We investigate three upper-plate earthquakes; the 10 April 2014 (M_w 6.1), 15 September 2016 (M_w 5.7), and 28 September 2016 (M_w 5.5), using Global Position System co-seismic displacements and relocated earthquake aftershocks. Our analyses of the three earthquakes indicate that the 10 April 2014 earthquake ruptured an unmapped margin-parallel right-lateral fault in Lago Xolotlán (Managua) and the September 2016 earthquakes ruptured arc-normal, left-lateral and oblique-slip faults. These earthquakes represent a triggered sequence whereby the 10 April 2014 earthquake promoted failure of the faults that ruptured in September 2016 by imparting a static Coulomb stress change (ΔCFS) of 0.02–0.07 MPa. Likewise, the 15 September 2016, earthquake additionally promoted failure (ΔCFS of 0.08–0.1 MPa) on sub-parallel faults that ruptured in two subsequent earthquakes. We also present an instance of magma-tectonic interaction whereby the 10 April 2014 earthquake dilated (10s of μStrain) the shallow magmatic system of Momotombo Volcano, which led to magma injection, ascent, and eruption on 1 December 2015, after ∼100 years of quiescence.