Location of Moderate-Sized Earthquakes Recorded by the NARS–Baja Array in the Gulf of California Region Between 2002 and 2006

Abstract

We relocated the hypocentral coordinates of small to moderate-sized earthquakes reported by the National Earthquake Information Center (NEIC) between April 2002 and August 2006 in the Gulf of California region and recorded by the broadband stations of the network of autonomously recording seismographs (NARS-Baja array). The NARS-Baja array consists of 19 stations installed in the Baja California peninsula, Sonora and Sinaloa, Mexico. The events reported by the preliminary determinations of epicenters (PDE) catalog within the period of interest have moment magnitudes (M w ) ranging between 1.1 and 6.7. We estimated the hypocentral location of these events using P and S wave arrivals recorded by the regional broadband stations of the NARS-Baja and the RESBAN (Red Sismolo´gica de Banda Ancha) arrays and using a standard location procedure with the HYPOCENTER code (LIENERT and HAVSKOV in Seism Res Lett 66:26-36, 1995) as a preliminary step. To refine the location of the initial hypocenters, we used the shrinking box source-specific station term method of LIN and SHEARER (J Geophys Res 110, B04304, 2005). We found that most of the seismicity is distributed in the NW-SE direction along the axis of the Gulf of California, following a linear trend that, from north to south, steps southward near the main basins (Wagner, Delfin, Guaymas, Carmen, Farallon, Pescadero and Alarcon) and spreading centers. We compared the epicentral locations reported in the PDE with the locations obtained using regional arrival times, and we found that earthquakes with magnitudes in the range 3.2-5.0 mb differ on the average by as much as 43 km. For the M w magnitude range between 5 and 6.7 the discrepancy is less, differing on the average by about 25 km. We found that the relocated epicenters correlate well with the main bathymetric features of the Gulf.

Space geodetic observation of the deformation cycle across the Ballenas Transform, Gulf of California

“…Our coseismic fault models have a rupture depth of 13 km, equivalent within uncertainties to the seismic estimates of 10-15 km for the base of earthquake nucleation along transforms in the Gulf of California [Munguia et al, 1977;Goff et al, 1987;Castro et al, 2010Castro et al, , 2011Sumy et al, 2013] but deeper than our estimates for the interseismic fault locking depth. Agreement between both parameters is not expected, Journal of Geophysical Research: Solid Earth 10.1002/2015JB011959 because the two approaches estimate the depth of the brittle-ductile transition zone over different time scales.…”

“…Our best fitting fault locking depth (between 11.7 ± 1.0 km in model 1 and 10.4 ± 1.5 km in model 2) is compatible with the base of seismicity at 10-15 km along transform faults in the northern and central Gulf of California [Goff et al, 1987;Castro et al, 2010Castro et al, , 2011Sumy et al, 2013]. Our model result only defines fault location at our GPS transection.…”

“…About~90% of the full North America-Pacific plate relative motion rate (approximately 43-47 mm/yr) is accommodated along the Gulf of California [DeMets et al, 1990[DeMets et al, , 1994DeMets and Dixon, 1999;Dixon et al, 2000a;Plattner et al, 2007Plattner et al, , 2009. Because of the submarine setting, however, crustal deformation studies have largely been limited to the interpretation of faulting processes that occur over short time scales in the seismogenic zone [Munguia et al, 1977;Goff et al, 1987;Rebollar et al, 2001;Rodriguez-Lozoya et al, 2008;Castro et al, 2010Castro et al, , 2011Sumy et al, 2013;Lopez-Pineda et al, 2014].…”

“…Red color indicates increased probability for failure, blue indicates decrease. The black dots are aftershocks fromCastro et al [2010]. The white star shows the location of the 2009 earthquake, and the green star shows the location of the 2012 M w 6.9 earthquake.…”

Remote triggered seismicity caused by the 2011, M9.0 Tohoku‐Oki, Japan earthquake

“…The swarm occurred during the following hours and continued for a couple of days after the passing of the waves (Figure 5). The earthquakes were located near a spreading center in the Farallon basin, a very active area in the Gulf of California where transform fault‐spreading center geometry is dominant [ Castro et al , 2011].…”