Rising sea levels are already having an impact on coastal inhabitants and exacerbating existing coastal threats including flooding during high tides and storm surges. According to new research, future sea-level rise will have an impact on the heights of future tsunamis. Over a billion people live in the coastal zone. Rising sea levels are already having an impact on coastal inhabitants and exacerbating existing coastal threats including flooding during high tides and storm surges.
However, new study by assistant professor Tina Dura and professor Robert Weiss of the College of Science’s Department of Geosciences suggests that future sea-level rise will have an impact on the heights of future tsunamis.
“Sea level will be much higher over the world in 50 to 70 years,” said Dura, who is also a member of the Fralin Life Sciences Institute’s Center for Coastal Studies. “If a tsunami strikes during that time period, the damages you’re anticipating for today will be larger. I believe that future models and hazards assessments should take sea-level rise into account by coastal geologists and modelers equally.”
Their findings were published in Nature Communications.
Tectonic plates collide with the enormous Pacific plate around the Ring of Fire, resulting in seismic and volcanic activity. Because the Pacific Ocean is surrounded by the Ring of Fire, massive earthquakes on its boundaries trigger localized tsunamis as well as distant-source tsunamis that propagate across the Pacific Ocean and devastate coastlines thousands of miles away.
Colliding tectonic plates off the coast of Alaska form the Alaska-Aleutian subduction zone, a 2500-mile-long fault. According to research, the subduction zone can generate distant-source tsunamis that strike the west coast of the United States, particularly Southern California.
The US Geological Survey launched a Science Application for Risk Reduction study in 2013 that focused on a distant-source tsunami that originated along the Alaska-Aleutian subduction zone and had an impact in California.
Sea level will be much higher over the world in 50 to 70 years. If a tsunami strikes during that time period, the damages you’re anticipating for today will be larger.
Assistant professor Tina Dura and Professor Robert Weiss
The experiment discovered that a magnitude 9.1 earthquake may cause a distant-source tsunami with an amplitude of 3.2 feet in the ports of Los Angeles and Long Beach, which would be greater than any previous distant-source tsunami at the ports, resulting in damages of up to $4.2 billion.
(a) Alaska map depicting parts of the Alaska-Aleutian subduction zone, earthquake boundaries, and historical earthquake extents. (b) The light gray shaded area depicts the USGS Science Application for Risk Reduction scenario magnitude 9.1 Semidi section earthquake. (c) A map of the Los Angeles and Long Beach ports shows the location of gauges that measure sea levels at the ports and maximum near-shore tsunami heights. (d) Plot of estimated earthquake magnitudes in the year 2000 without tidal variability (blue histogram), with tidal variability (green histogram), and combined tsunami heights and tidal variability (red histogram) (red histogram).
This tsunami scenario at the ports of Los Angeles and Long Beach, however, will not be realistic in the long run due to rising sea levels. Temperatures around the world are rising, and sea levels are rising as well, according to observations. The question is not whether sea level will continue to rise, but how much.
Dura and Weiss collaborated with colleagues from Rowan University, Rutgers University, Durham University, Nanyang Technological University, and the United States Geological Survey to examine how rising sea levels will affect tsunami heights in Southern California using distant-source tsunami modeling and future sea-level rise projections.
The group forecasted sea-level rise for the ports of Los Angeles and Long Beach using scenarios that included both low and high estimates of greenhouse gas emissions and climate change mitigation options.
Mitigation techniques to minimize greenhouse gas emissions were included in one scenario, resulting in little temperature and sea-level rise. Another scenario depicts a future with no mitigation initiatives and large emissions, resulting in quicker temperature rises and greater sea levels.
The scientists discovered that currently, a magnitude 9.1 earthquake can generate wave heights of more than 3.2 feet in the ports. However, under high-emissions sea-level rise forecasts, a considerably weaker magnitude 8 earthquake will be able to generate a tsunami of more than 3.2 feet by 2100.
In other words, rising sea levels render ports more vulnerable to tsunamis caused by weaker earthquakes. The findings are particularly troubling given the increased frequency of magnitude 8 earthquakes.
“A 9.1 is really rare,” Dura remarked. “So, today, the chances of a tsunami reaching 3.2 feet at the ports are extremely low because a very rare, extremely strong earthquake would be necessary. However, due to rising sea levels, a magnitude 8 earthquake, which occurs frequently along the Pacific Rim, will be able to exceed the same tsunami heights in 2100.”
“This work clearly demonstrates the potential for future tsunamis to become significantly more destructive as sea levels rise, especially if we fail to curb future greenhouse gas emissions,” said co-author Andra Garner, an assistant professor at Rowan University who studies sea-level rise. “The good news is that the research also shows our capacity to reduce future threats if we act to limit future warming and the amount by which future sea levels rise.”
However, knowing about these potentially devastating tsunamis necessitates not just looking ahead, but also looking back. The US Geological Survey Science Application for Risk Reduction project exclusively investigated earthquakes that occurred inside the Alaska-Aleutian subduction zone’s Semidi sector. But since that initial work, Dura and colleagues have published research that suggests other sections of the subduction zone should be considered as well.
Historical earthquakes have occurred in the Semidi and neighboring Kodiak sections of the subduction zone. A magnitude 8.3 earthquake rocked the Semidi region in 1938. A magnitude 9.2 earthquake rocked the Kodiak area and adjoining portions to the east in 1964, the strongest recorded earthquake on the Alaska-Aleutian subduction zone.
Because the earthquakes of 1938 and 1964 did not overlap, the area between them was identified as a “permanent earthquake border” on seismic hazard maps. In other words, the risk of the region’s largest, multi-section earthquakes was regarded as fairly low.
“Although the 1964 earthquake rupture did not cross into the 1938 earthquake rupture area, it is unknown if this has been the case for earthquakes hundreds to thousands of years before. Should this be seen as a permanent barrier between earthquakes, or can very massive, multi-section earthquakes occur in this region? We were curious, so we set out to find out “Dura stated.
Dura and colleagues utilized 5 centimeter cookie-cutter-like cylinders to gather core samples from wetlands scattered across the predicted earthquake boundary to learn more about the seismic history of the Alaska-Aleutian subduction zone.
The team next examined the soil layers in the cores to find instances of land-level shift and wave inundation caused by previous earthquakes. The team was able to create a history of past big earthquakes in the region using radiocarbon, cesium, and lead dating. Their investigation revealed that many big earthquakes had crossed the hypothesized seismic barrier, implying that earthquakes that ruptured both the Semidi and Kodiak parts of the subduction zone had happened previously.
“Our geologic data indicates that earthquakes can cross the Semidi and Kodiak sections,” Dura stated. “As a result, we included both single and multi-section earthquakes in our port distant-source tsunami modeling. We feel that by integrating multi-section earthquakes in our models, the range of tsunami heights we anticipate for the ports advances our understanding of the implications of future tsunamis there.”
The group’s findings will be used to improve future modeling scenarios for the Alaska-Aleutian subduction zone by including it in danger maps for southern Alaska.
