资源环境科技发展态势分析平台

A fundamental question of earthquake science is what produces damaging high-frequency ground motion, with the classic Brune-Haskell model postulating that abrupt fault slip causes it. However, even when amended with heterogeneous rupture, the model fails to explain observations of different sized repeating earthquakes and has challenges explaining high-frequency radiation patterns. We propose an additional cause for high-frequency earthquake spectra from elastic collisions of structures within a rupturing fault zone. The collision spectrum is set by an impact contact time proportional to the size of colliding structures so that spectra depend on fundamentally different physical parameters compared with slip models. When added to standard models, collisions can reconcile the discrepant observations since the size, shape, and orientation of structures vary between different fault zones but remain constant within a fault segment. High-frequency earthquake ground motions and damage may therefore be an outgrowth of fault-zone structure rather than sudden initiation of slip.

Plain Language Summary Why do earthquakes damage buildings? Many buildings are damaged most heavily by fast, jerky ground motion rather than the longer duration rolling motions that contain most of the earthquake energy. Despite the importance of these fast, jerky motions, most frictional models for earthquakes generally underpredict how strong they are, even when heterogeneous friction and realistic roughness are accounted for. We propose that collisions of structures as they attempt to slide past each other during an earthquake may also create jerky ground motion. We find that the ground motion from collisions depends mostly on the size of the structures and does not depend on stresses within the Earth and thus gives a very different interpretation of what causes the most damaging ground motions. When incorporated with standard frictional models, the collision model explains various observations that are otherwise difficult to explain, including why some earthquakes appear to be identical in time but with larger amplitudes, why faults that have had many earthquakes have less damaging ground motions, and why earthquake damage is observed to occur more uniformly than previously predicted.