jIn this thesis, seismic waves generated by sources rangi ng from 2.7 kg shots of TNT to magni tude 5 earthquakes are studied in order to determine the seismic activity and crustal structure of the Orozco transform fault. Most of the data were coll ected by a network of 29 ocean bottom seismometers (OBS) and hydrophones (OBH) which were deployed as part of project ROSE (Rivera Ocean Seismic Experiment). Additional information is provided by magnetic anomaly and bathymetric data collected during and prior to ROSE and by teleseismic earthquakes recorded by the WWSSN (Worldwide Seismic Station Network).In Chapter II, the tectonic setting, bathymetry and teleseismic history of the Orozco Fracture Zone are summari zed. Coveri ng an area of 90 x 90 km whi ch i ncl udes ridges and troughs trending both parallel and perpendicular to the present spreading direction (approximately east-west), the bathymetry of the transform portion of the fracture zone does not resemble that of other transform faults which have been studied in detail. A detailed study of one of the largest teleseismic earthquakes (mb=5.1) indicates right lateral strike-slip faulting with a strike parallel to the present spreading direction and a focal depth of less than 5 km. The moment sum from teleseismic earthquakes suggests an average fault width of at most a few kilometers. Because the teleseismic earthquake locations are too imprecise to define the present plate boundary and the magnetic anomaly data are too sparse to resolve the recent tectonic history, more questions are raised than are answered by the results in this chapter. These questions provide the focus for the study of the ROSE data. Chapter III contains an examination of the transfer function between seafloor motion and data recorded by the MIT OBS. The response of the recordi ng system is determi ned and the coupl i ng of the OBS to the seafloor duri ng tests at two nearshore sites is analysed. Applying these results to the ROSE data, we conclude that the ground motion in the absence of the instrument can be adequately determi ned for at 1 east one of the MIT OBS deployed duri ng ROSE.Hypocentral parameters for 70 earthquakes, calculated for a n ass u m ê d 1 ate r a 11 y h 0 m 0 g e n e 0 u s vel 0 city s t r u c t u r e w h i c h was adapted from the results of several refraction surveys in the area, are presented in Chapter iv. Because of the large number of stations in the ROSE network, the epicentral 1 ocati ons, focal depths and source mechani sms are determi ned with a precision unprecedented in marine microseismic work.Relative to the assumed model, most horizontal errors are less than I1 km; vertical errors are somewhat larger. All epicenters are within the transform region of the Orozco Fracture Zone. About half of the epicenters define a narrow 1 i n e 0 f act i vi ty par a 11 e 1 to the s p rea din g d ire c t i ~ n and situated along a deep topographic trough which forms the northern boundary of the transform zone (region 1). Most well determined depths are very sha...