Focal mechanisms and magnitude distributions

of “off-fault” earthquakes

David D. Jackson, Yan Kagan, and Qi Wang, UCLA

Stefan Hiemer, ETH Zurich

Focal mechanisms• At each point, assumed moment

tensor is weighted sum of those for nearby earthquakes and fault elements

• Weighting inversely proportional to distance

• For moment tensors on faults, weighting proportional to moment rate on fault element.

Earthquake catalog,

magnitude 4.7+, 1850 -

2009

Representation of larger events as sums of

subevents

Earthquake and fault proximity

Projection of fault surface, and weighting scheme

Focal mechanisms derived from earthquakes and faults,

respectively

Optimization of seismicity/fault weighting and smoothing distance

Magnitude distribution for all quakes, and quakes on faults

Expected size limit depends on time window.