Probabilistic Quantification of Tsunami Currents in Karachi Port, Makran
Subduction Zone, using Statistical Emulation
Abstract
In this paper, we model the full range of possible local impacts of
future tsunamis in the Makran subduction zone (MSZ) at Karachi port,
Pakistan. For the first time, the 3-D subduction geometry Slab2 is
employed in the MSZ, in conjunction with the most refined rupture
segmentation to date for this region, to improve the earthquake source
definition. Motivated by the massive sediment layer over the MSZ, we
also introduce to tsunami modeling the application of the sediment
amplification formula, resulting in enhancements of seabed deformation
up to 60% locally. Furthermore, we design a new unstructured mesh
algorithm for our GPU-accelerated tsunami code in order to efficiently
represent flow velocities, including vortices, down to a resolution of
10m in the vicinity of the port. To afford to compute very large number
of high resolution tsunami scenarios, for the granularity and extent of
the range of magnitudes (occurrence ratios of 1:100,000 implied by the
Gutenberg-Richter relation) and locations of source, we create a
statistical surrogate (i.e. emulator) of the tsunami model. Our main
contribution is hence the largest set of emulated predictions using any
realistic tsunami code to date: 1 million per location. We go on to
obtain probabilistic representations of maximum tsunami velocities and
heights at around 200 locations in the port area of Karachi. Amongst
other findings, we discover substantial local variations of currents and
heights. Hence we argue that an end-to-end synthesis of advanced
physical, numerical and statistical modeling is instrumental in coastal
engineering to comprehensively model local impacts of tsunamis.