THE APRIL 22, 1991, VALLE-DE-LA-ESTRELLA, COSTA-RICA (MW = 7.7) EARTHQUAKE AND ITS TECTONIC IMPLICATIONS - A BROAD-BAND SEISMIC STUDY - GOES,SDB; VELASCO,AA; SCHWARTZ,SY; LAY,T (JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 1993)