Study inspired by 2010 tsunami yields findings that fly in the face of generations of common wisdom
A long-held belief that offshore islands protect the mainland from tsunamis turns out to be the exact opposite of the truth, according to a new study.
Common wisdom -- from Southern California to the South Pacific -- for coastal residents and scientists alike has long been that offshore islands would create a buffer that blocked the power of a tsunami. In fact, computer modeling of tsunamis striking a wide variety of different offshore island geometries yielded no situation in which the mainland behind them fared better.
Instead, islands focused the energy of the tsunami, increasing flooding on the mainland by up to 70 percent.
"This is where many fishing villages are located, behind offshore islands, in the belief that they will be protected from wind waves. Even Southern California residents believe that the Channel Islands and Catalina will protect them," said Costas Synolakis of the USC Viterbi School of Engineering, a member of the multinational team that conducted the research.
The research was inspired by a field survey of the impact of the 2010 tsunami on the Mentawai Islands off of Sumatra. The survey data showed that villages located in the shadow of small offshore islets suffered some of the strongest tsunami impacts, worse than villages located along open coasts.
Subsequent computer modeling by Jose Borrero, adjunct assistant research professor at the USC Viterbi Tsunami Research Center, showed that the offshore islands had actually contributed to -- not diminished -- the tsunami's impact.
Synolakis then teamed up with researchers Emile Contal and Nicolas Vayatis of Ecoles Normales de Cachan in Paris; and Themistoklis S. Stefanakis and Frederic Dias, who both have joint appointments at Ecoles Normales de Cachan and University College Dublin to determine whether that was a one-of-a-kind situation, or the norm.
Their study, of which Dias was the corresponding author, was published in Proceedings of the Royal Society A on Nov. 5.
The team designed a computer model that took into consideration various island slopes, beach slopes, water depths, distance between the island and the beach, and wavelength of the incoming tsunami.
"Even a casual analysis of these factors would have required hundreds of thousands of computations, each of which could take up to half a day," Synolakis said. "So instead, we used machine learning."
Machine learning is a mathematical process that makes it easier to identify the maximum values of interdependent processes with multiple parameters by allowing the computer to "learn" from previous results.
The computer starts to understand how various tweaks to the parameters affect the overall outcome and finds the best answer quicker. As such, results that traditionally could have taken hundreds of thousands of models to uncover were found with 200 models.
"This work is applicable to some of our tsunami study sites in New Zealand," said Borrero, who is producing tsunami hazard maps for regions of the New Zealand coast. "The northeast coast of New Zealand has many small islands offshore, similar to those in Indonesia, and our modeling suggests that this results in areas of enhanced tsunami heights."
"Substantial public education efforts are needed to help better explain to coastal residents tsunami hazards, and whenever they need to be extra cautious and responsive with evacuations during actual emergencies," Synolakis said.
The research was funded by EDSP of ENS-Cachan; the Cultural Service of the French Embassy in Dublin; the ERC; SFI; University College Dublin; and the EU FP7 program ASTARTE. The study can be found online at http://rspa.royalsocietypublishing.org/content/470/2172/20140575
Robert Perkins | EurekAlert!
GPM sees deadly tornadic storms moving through US Southeast
01.12.2016 | NASA/Goddard Space Flight Center
Cyclic change within magma reservoirs significantly affects the explosivity of volcanic eruptions
30.11.2016 | Johannes Gutenberg-Universität Mainz
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water
In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...
The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.
Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
02.12.2016 | Medical Engineering
02.12.2016 | Agricultural and Forestry Science
02.12.2016 | Physics and Astronomy