The 1990 Lake Tennyson earthquake sequence, Marlborough, New Zealand

Abstract

Aftershocks from the 1990 Lake Tennyson earthquake (M_L 5.8) recorded at nine temporary portable seismographs have been used to invert travel‐time data simultaneously for both hypocentre and velocity parameters, resulting in a 1‐D velocity model and station terms for the Lake Tennyson region. The distribution of the best relocated aftershocks outlines a main fault lineation in a ENE direction, and several off‐fault clusters. The main fault lineation is 8 km long, with a strike of about 60° and a dip that is nearly vertical. It is located between and subparallel to the Awatere and Fowler Faults, on a previously unknown fault. The mainshock has been relocated in the middle of this lineation zone, which suggests that the fault ruptured bilaterally. The distribution of aftershocks matches that expected from the Coulomb failure criterion, which identifies areas of increased and decreased stress levels due to the occurrence of the mainshock. Focal mechanisms for the mainshock and aftershocks that make up the main fault lineation are consistent with right‐lateral strike‐slip movement on this fault. Clusters that extend from each end of the main fault lineation predominantly do not have strike‐slip focal mechanisms. Aftershocks located in the clusters to the north of the main fault lineation have various thrust mechanisms with no consistent orientation. Most focal mechanisms from this sequence had their P axes closely aligned with the regional axis of compression, and the main fault lineation is consistent with the relative plate motion direction in the Lake Tennyson region.