J. Braunmiller et al., THE 1993 KLAMATH-FALLS, OREGON, EARTHQUAKE SEQUENCE - SOURCE MECHANISMS FROM REGIONAL DATA, Geophysical research letters, 22(2), 1995, pp. 105-108
We use regional broadband seismograms to obtain seismic moment-tenser
solutions of the two September 20, 1993, M(w)=6, Klamath Falls, Oregon
earthquakes, their foreshock and largest aftershocks (M(D)>3.5). Seve
ral sub-groups with internally consistent solutions indicate activity
on several fault segments and faults. From the estimated moment-tensor
s and depths of the main shocks and from the aftershock distribution w
e deduce that both main shocks occurred on an east-dipping normal faul
t, possibly related to the Lake of the Woods fault system. Rotation of
T-axes between the two main shocks is consistent with the two dominan
t trends of the aftershocks and mapped faults. We propose that a chang
e in fault strike acted as temporary barrier separating the rupture of
the main shocks. Empirical Green's function analysis shows that the f
irst main event had a longer rupture duration (half-duration 1.7 s) th
an the second (1.2 s). In December, vigorous shallow activity commence
d near Klamath Lake's western shore, 5-10 km east of the primary after
shock zone. It appears a M(w)=5.5 aftershock occurring the day before,
though within the primary aftershock zone, triggered the activity.