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Castro, RR, Valdes-Gonzalez C, Shearer P, Wong V, Astiz L, Vernon F, Perez-Vertti A, Mendoza A.  2011.  The 3 August 2009 M-w 6.9 Canal de Ballenas Region, Gulf of California, Earthquake and Its Aftershocks. Bulletin of the Seismological Society of America. 101:929-939.   10.1785/0120100154   AbstractWebsite

On 3 August 2009 an earthquake of magnitude M-w 6.9 occurred near Canal de Ballenas, in the north-central region of the Gulf of California, Mexico. The focal mechanism of the main event, reported in the Global Centroid Moment Tensor (CMT) catalog, is right lateral strike-slip with a strike of 216 degrees and a dip of 78 degrees. The initial location reported by the National Seismological Service of Mexico [Servicio Sismologico Nacional (SSN)] and the Array Network Facility (ANF) suggested that the epicenter was on the North American plate near the Tiburon fault, which is considered inactive. This earthquake was preceded by a magnitude m(b) 5.5 event that occurred about 5 min before. In the next 40 min after the main event two aftershocks with magnitudes m(b) 4.9 and M-w 6.2 occurred, and on 5 August a third aftershock of M-w 5.7 was located in the Canal de Ballenas region. The events of August 2009 were recorded by the regional stations of the broadband network Red Sismologica de Banda Ancha (RESBAN) that Centro de Investigacion Cientifica y de Educacion Superior de Ensenada (CICESE) operates and by stations of the SSN also located in the region of the Gulf of California. We used body-wave arrivals to determine precise epicentral locations and to estimate the rupture area of this important sequence of earthquakes. The resulting hypocentral coordinates indicate that the main event of this sequence occurred along the Canal de Ballenas transform fault, with a rupture length of 50 km. Based on the aftershock distribution, we estimate that the main event had a rupture area of approximately 600 km(2), an average slip of 1.3 m, and a stress drop of 2.2 MPa.

Castro, RR, Shearer PM, Astiz L, Suter M, Jacques-Ayala C, Vernon F.  2010.  The Long-Lasting Aftershock Series of the 3 May 1887 M-w 7.5 Sonora Earthquake in the Mexican Basin and Range Province. Bulletin of the Seismological Society of America. 100:1153-1164.   10.1785/0120090180   AbstractWebsite

We study local and regional body-wave arrival times from several seismic networks to better define the active regional fault pattern in the epicentral region of the 3 May 1887 M-w 7.5 Sonora, Mexico (southern Basin and Range Province) earthquake. We determine hypocenter coordinates of earthquakes that originated between 2003 and 2007 from arrival times recorded by the local network RESNES (Red Sismica del Noreste de Sonora) and stations of the Network of Autonomously Recording Seismographs (NARS)-Baja array. For events between April and December 2007, we also incorporated arrival times from USArray stations located within 150 km of the United States-Mexico border. We first obtained preliminary earthquake locations with the Hypoinverse program (Klein, 2002) and then relocated these initial hypocenter coordinates with the source-specific station term (SSST) method (Lin and Shearer, 2005). Most relocated epicenters cluster in the upper crust near the faults that ruptured during the 1887 earthquake and can be interpreted to be part of its long-lasting series of aftershocks. The region of aftershock activity extends, along the same fault zone, 40-50 km south of the documented southern tip of the 1887 rupture and includes faults in the epicentral region of the 17 May 1913 (I-max VIII, M-I 5.0-0.4) and 18 December 1923 (I-max IX, M-I 5.7-0.4) Granados-Huasabas, Sonora, earthquakes, which themselves are likely to be aftershocks of the 1887 event. The long aftershock duration can be explained by the unusually large magnitude of the mainshock and by the low slip rates and long mainshock recurrence times of the faults that ruptured in 1887.

Collins, JA, Vernon FL, Orcutt JA, Stephen RA, Peal KR, Wooding FB, Spiess FN, Hildebrand JA.  2001.  Broadband seismology in the oceans: Lessons from the Ocean Seismic Network Pilot Experiment. Geophysical Research Letters. 28:49-52.   10.1029/2000gl011638   AbstractWebsite

The fundamental objective of the Ocean Seismic Network Pilot Experiment (OSNPE) - which was carried out over a period of about 4 months at a site 225 km southwest of Oahu, Hawaii - was to learn how to make high-quality, broadband seismic measurements in the deep oceans. The OSNPE results demonstrate that broadband data of quality similar to that of quiet land stations can be acquired with seafloor seismographs, but that the location of the seismometer - whether it be on the seafloor, surficially buried within the seabed, or in a deep borehole - has a profound effect on data quality. At long-periods (< 0.1 Hz), data quality was highest for a seismometer buried just beneath the seafloor, while at short-periods (> 0.1 Hz), data quality was best for a seismometer deployed 242 m below the seafloor in a borehole.

Collins, JA, Vernon FL, Orcutt JA, Stephen RA.  2002.  Upper mantle structure beneath the Hawaiian swell: Constraints from the ocean seismic network pilot experiment. Geophysical Research Letters. 29   10.1029/2001gl013302   AbstractWebsite

[1] Data from two broadband, ocean-bottom seismographic stations deployed similar to 225 km southwest of Oahu, Hawaii during the Ocean Seismic Network Pilot Experiment provide constraints on upper mantle structure beneath the Hawaiian swell. Receiver functions show that the mantle transition zone is thinned by >50 km relative to reference model PA5, which, in the absence of compositional changes, implies excess temperatures of >350 K in the transition zone. The combination of the measurements reported here and the thickness variations reported by Li et al. [2000] imply that the transition zone is thinned by 30 +/- 15 km over an along-swell dimension of at least 700 km. At similar to80 km depth, P-to-S converted phases are identified from the Gutenberg discontinuity marking the lid of the oceanic low-velocity zone and the base of the lithosphere. Shear-wave splitting measurements imply that fast-polarization azimuths are intermediate between the absolute plate-motion vector and the fossil spreading direction; multi-event stacked values of o and deltat are -80degrees and 1.5 s, respectively.