Fault plane solutions from first motion polarity of P-waves give two nodal planes among which it is not possible to distinguish the fault plane from the auxiliary one. We found that, for earthquakes recorded by a dense local network, it is possible to identify the rupture direction from the Doppler effect produced by directivity. This principle was successfully applied, using three different simple techniques (direct inspection and time and frequency domains analyses), to one ML 3.6 and six smaller (1.2≤ML≤2.0) well-recorded earthquakes from northern Baja California, Mexico. The results indicate activity in faults conjugate to those currently mapped in this region.

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