Mud volcano response to the 4 April 2010 El Mayor-Cucapah earthquake

Mud volcanoes sometimes respond to earthquakes, but the mechanisms by which earthquakes trigger changes in ongoing eruptions or initiate new eruptions are not completely understood. We measured gas discharge at a field of mud volcanoes near the Salton Sea, southern California, before and after the 4 April 2010 El Mayor-Cucapah earthquake and observed an increase in gas flux immediately following the earthquake and a subsequent recovery to pre-earthquake values. This earthquake-eruption pair is of particular interest because the earthquake produced large strains, up to 1.2%, near the mud volcano location, allowing us to test two competing triggering mechanisms: (1) shaking-induced bubble mobilization and (2) permeability enhancement. We measured the rheology of erupted mud from the mud volcanoes to quantify the importance of mechanism 1 and found that this mechanism is unlikely to be important. We therefore favor the explanation that the increased gas flux was caused by a transient increase in permeability.