Megathrust reflectivity reveals the updip limit of the 2014 Iquique earthquake rupture

The updip limit of seismic rupture during a megathrust earthquake exerts a major control on the size of the resulting tsunami. Offshore Northern Chile, the 2014 Mw 8.1 Iquique earthquake ruptured the plate boundary between 19.5 degrees and 21 degrees S. Rupture terminated under the mid-continental slope and did not propagate updip to the trench. Here, we use state-of-the-art seismic reflection data to investigate the tectonic setting associated with the apparent updip arrest of rupture propagation at 15 km depth during the Iquique earthquake. We document a spatial correspondence between the rupture area and the seismic reflectivity of the plate boundary. North and updip of the rupture area, a coherent, highly reflective plate boundary indicates excess fluid pressure, which may prevent the accumulation of elastic strain. In contrast, the rupture area is characterized by the absence of plate boundary reflectivity, which suggests low fluid pressure that results in stress accumulation and thus controls the extent of earthquake rupture. Generalizing these results, seismic reflection data can provide insights into the physical state of the shallow plate boundary and help to assess the potential for future shallow rupture in the absence of direct measurements of interplate deformation from most outermost forearc slopes. The rupture area of the 2014 Iquique earthquake offshore northern Chile was spatially limited to a region where the plate boundary is non-reflective in seismic images, indicative of low fluid pressure. In contrast, north and updip of the rupture area, a coherent highly reflective plate boundary indicates excess fluid pressure, which may inhibit strain accumulation, while strain release in the non-reflective rupture area occurs during large earthquakes.

Automated summary

The updip limit of seismic rupture plays a major role in determining the size of a tsunami caused by a megathrust earthquake. Using seismic reflection data, researchers have found that the rupture area of the 2014 Iquique earthquake in offshore Northern Chile was characterized by low fluid pressure, while north and updip of the rupture area, there was excess fluid pressure. This knowledge can help assess the potential for future shallow rupture and improve understanding of the physical state of shallow plate boundaries.