Earthquakes of similar magnitude can trigger tsunamis of greatly differing sizes. This commonly observed, however not well-understood phenomenon has hindered trusted cautions of regional tsunamis.
Research led by University of Hawaii (UH) at Manoa scientists offers brand-new insight that links the attributes of earthquakes– magnitude, depth where 2 tectonic plates slip past each other and the rigidity of the plates involved– with the possible size of a resulting tsunami.
Previous scientists recognized an unique class of events known as tsunami earthquakes, which produce disproportionately large tsunamis for their magnitude. Kwok Fai Cheung, teacher of Ocean and Resources Engineering in the UH Manoa School of Ocean and Earth Science and Technology (SOEST), Thorne Lay from the University of California– Santa Cruz, and co-authors discovered a straightforward explanation for this dilemma. On September 29, 2009, a tsunami triggered significant damage and loss of life in American Samoa, Samoa, and Tonga. The tsunami was generated by a large earthquake in the Southern Pacific Ocean.
Previous researchers recognized a special class of occasions understood as tsunami earthquakes, which produce disproportionately large tsunamis for their magnitude. Kwok Fai Cheung, teacher of Ocean and Resources Engineering in the UH Manoa School of Ocean and Earth Science and Technology (SOEST), Thorne Lay from the University of California– Santa Cruz, and co-authors found a simple explanation for this quandary. Their findings were released recently in Nature Geoscience.
Graphic showing how a tsunami works. Credit: Ocean Institute, modified by NOAA/ NWS/ CGS
Using computer designs, the team incorporated physical processes that produce earthquakes and tsunamis with a wide range of observations of real-world occasions, consisting of those classified as tsunami earthquakes. The design results demonstrated that for a given earthquake magnitude, if the rupture extends to shallow depth in the less rigid part of the plate, the resulting tsunami is larger than if the rupture is much deeper.
” In a subduction zone, the upper plate is thinner and less stiff than the underthrusting plate near the trench,” described Cheung. “A concentrated near-trench or shallow rupture produces fairly weak ground shaking as taped by seismometers, but the displaced water in the overlying deep ocean has actually boosted energy and produces shorter tsunami waves that amplify at a high rate as they move towards the coast.”
” Earthquake and tsunamigenic procedures are complicated, including many elements that differ from one event to another,” said Lay, professor of Earth and Planetary Sciences at UC Santa Cruz. “We utilized a simplified mathematical design to separate crucial earthquake criteria and assess their significance in defining tsunami size.”
On September 29, 2009, a tsunami triggered significant damage and loss of life in American Samoa, Samoa, and Tonga. The tsunami was created by a large earthquake in the Southern Pacific Ocean. Credit: NOAA
Having confirmed that the existence of shallow earthquake rupture can be a more considerable aspect than the earthquake magnitude for the resulting tsunami size led the scientists to an essential concern: Can earthquake magnitude continue to be used as the main indication of possible tsunami impacts?
” The practice of utilizing earthquake magnitude to estimate possible tsunami hazard has resulted in poor predictive ability for tsunami impacts, and more details about the source is required to do better,” stated Cheung.
An important aspect of this interdisciplinary research study is the synergy of proficiency in seismology, with Lay, and tsunamis, with Cheungs research group, applied to a large set of observations. This research study motivates advancement of brand-new seismological and seafloor geodesy research study that can quickly identify the event of shallow rupture in order to attain more dependable tsunami warning.
While coastlines throughout the Pacific Ocean and along the “Ring of Fire” are vulnerable to tsunamis, the circumstance is most critical for seaside neighborhoods near the earthquake, where the tsunami shows up rapidly– when detailed details about the earthquake is not yet available.
Cheung and Lay continue their partnership to investigate prehistorical, historic, and future tsunami occasions to better understand the risks presented to seaside neighborhoods and allow more precise warning systems.
Reference: “Tsunami size irregularity with rupture depth” by Kwok Fai Cheung, Thorne Lay, Lin Sun and Yoshiki Yamazaki, 13 December 2021, Nature Geoscience.DOI: 10.1038/ s41561-021-00869-z.