We investigate the directivity of three well-recorded repeating sequences of earthquakes (M2-3, 2001–2016) on the San Andreas Fault at Parkfield (California) that are well-recorded by a borehole network.

We calculate rupture directivity and velocity from P waves using the empirical Green’s function method. The individual events in each sequence all show the same directivity; those in the largest magnitude sequence (M~2.7, 8 events) rupture unilaterally to the NW (at ~0.8V_s), those in the second sequence (M~2.3, 9 events) rupture unilaterally to the SE, and those of smallest magnitude sequence (M~2, 11 events) are less well resolved.

The source spectra of the M~2.7 sequence exhibit no detectable temporal variation. The M~2 sequence exhibits a decrease in high frequency energy following the M6 event, that recovers with time, implying a decrease in stress drop then gradual healing. The third sequence (M~2.3) shows a similar, less well resolved response to the M6.