Dike-induced faulting and graben subsidence in volcanic rift zones

Field observations and geodetic data indicate that dike intrusion in volcanic rift zones typically generates normal faulting and graben subsidence at the Earth's surface. Dike intrusion increases the horizontal compression adjacent to the dike and decreases the compression beyond the dike perimeter. Therefore fault slip extending to the dike plane is most likely to occur above or in front of the laterally propagating dike. Two data sets documenting the change in surface elevation accompanying dike intrusion in the Krafla rift zone, Iceland, were inverted to determine the dike and fault geometry at depth. Results indicate that fault slip in front of the dike is capable of producing most of the subsidence observed. Additional subsidence could result from reasonable mechanical anisotropy of the rift zone. -from Author