An Introduction to Non-Double-Couple Sources

Robert Anthony Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology Abstract Since the early 1960s when Maruyama and Burridge and Knopoff convincingly demonstrated that the elastodynamic radiation patterns exhibited by shear faulting in an isotropic, elastic medium were consistent with a pair of force couples, it has become standard practice amongst seismologists to assume that all earthquakes originate from this force system. This premise carries with it the assumptions that all earthquakes are occurring on shear faults, have trivial isotropic components, and can be described by a symmetric strain tensor. However, as the global seismic network has expanded and as data quality has improved, earthquake sources have been discovered that cannot be adequately described by a simple double-couple force system. Such earthquakes are described as having non-double-couple sources. Yet many seismologists continue to quantitatively analyze earthquakes without considering non-double-couple components. This paper is intended to introduce non-double-couple sources and analysis techniques and convincingly demonstrate that non-double-couple components should be acknowledged during earthquake source studies.