The 1080 AD earthquake between Mainz and Speyer (Upper Rhine Graben, Germany) – archeoseismology allows relocating the epicentre

The imposing Romanesque cathedral of Speyer (Upper Rhine Graben, Germany) was built as thr burial site of German emperors, consecrated in AD 1061. However, mere two decades later it was almost completely rebuilt, a very unusual step in the history of any church. We put forward the hypothesis that the cathedral was severely damaged by an earthquake making re-building necessary. We describe construction history, identify features of earthquke-induced damage, and describe engineering solutions to make the new building more resistant to seismic shaking. An intensity IX-X is assigned based on archeoseismological evidence. The AD 1080 earthquake, recorded in Mainz (ESI-2007 = VII-VIII), some 80 km to the north, was probably the culprit. We suggest to relocate the epicentre from the proximity of Mainz southward, towards Speyer, with an M6.5 magnitude. ShakeMap analysis supports lower intensity for Mainz and higher intensity for Speyer. Worms cathedral, located halfway between Mainz and Speyer, bears evidence for destructive earthquake with severely tilted walls, which necessitated the rebuilding of collapsed vaults. Damage to the choir and apsis are very similar to those of Speyer. Start of the construction is known to be some time before 1132-37 AD. Whether this was the same earthquake which damaged Speyer, needs further considerations. Archaeoseismology provides information about past earthquakes which lack proper historical documentation.