Consideration of rupture kinematics increases tsunami amplitudes in far-field hazards assessments

Diego Melgar 

Tsunamis are large surges of sea water caused by undersea earthquakes. To prepare for future tsunamis, scientists run computer simulations to estimate how big the waves might be and how often they could happen. These simulations are used to make maps and design buildings that can withstand tsunami impacts. Most of these models assume that when an earthquake breaks a fault this happens all at once. But in reality, earthquakes unfold over time—sometimes taking several minutes to rupture hundreds of miles of fault. This study shows that the way an earthquake a fault (called "rupture kinematics") can change the size and timing of the tsunami waves that reach faraway places, like Hawaii or the U.S. West Coast. By modeling thousands of possible earthquakes along Alaska’s subduction zone, we found that accounting for the way earthquakes move along the fault can make the tsunami waves significantly larger—especially for very big earthquakes. In some cases, ignoring this time evolution could underestimate the impacts by 30\% or more. This means current tsunami hazard assessments may be biased low. To better prepare for future tsunamis, we recommend updating how these assessments are done to include more realistic earthquake behavior.