Focal mechanisms of the March 6, 1987 Ecuador earthquakes - CMT inversion with
a first motion constraint,
Kawakatsu, H., and G. P. Cadena
J. Phys. Earth, 39,
589-597, 1991.
For a shallow earthquake $M sub {r theta}$ and $M sub {r phi}$ components of
a moment tensor are difficult to constrain using long-period data only
(Kanamori and Given, 1981).
Many researchers have attempted to circumvent this difficulty by incorporating
either first motion polarity data (e.g., Nakanishi and Kanamori, 1984;
Michael and Geller, 1984; Tanimoto and Kanamori, 1986; Suetsugu
and Nakanishi, 1988) or shorter-period
bodywave waveforms ($Ekstr o dotdot m$, 1987; Honda and Seno, 1989).
In this short report we present a new method to incorporate first motion
polarity data with the centroid moment tensor (CMT) inversion
of Dziewonski et al. (1981) and apply it to large shallow earthquakes
which occurred in Ecuador.