A study of the 2015 Mw 8.3 Illapel earthquake and tsunami: Numerical and analytical approaches

The September 16, 2015 Illapel, Chile earthquake
triggered a large tsunami, causing both economic losses and
fatalities. To study the coastal effects of this earthquake, and to
understand how such hazards might be accurately modeled in the
future, different finite fault models of the Illapel rupture are used to
define the initial condition for tsunami simulation. The numerical
code Non-hydrostatic Evolution of Ocean WAVEs (NEOWAVE)
is employed to model the tsunami evolution through the Pacific
Ocean. Because only a short time is available for emergency
response, and since the earthquake and tsunami sources are close to
the coast, gaining a rapid understanding of the near-field run-up
behavior is highly relevant to Chile. Therefore, an analytical
solution of the 2 ? 1 D shallow water wave equations is considered.
With this solution, we show that we can quickly estimate the
run-up distribution along the coastline, to first order. After the
earthquake and tsunami, field observations were measured in the
surrounded coastal region, where the tsunami resulted in significant
run-up. First, we compare the analytical and numerical solutions to
test the accuracy of the analytical approach and the field observations,
implying the analytic approach can accurately model tsunami
run-up after an earthquake, without sacrificing the time necessary
for a full numerical inversion. Then, we compare both with field
run-up measurements. We observe the consistency between the two
approaches. To complete the analysis, a tsunami source inversion is
performed using run-up field measurements only. These inversion
results are compared with seismic models, and are shown to capture
the broad-scale details of those models, without the necessity of the
detailed data sets they invert.