Guadalajara, Mexico, Earthquake Sequence of December 2015 and May 2016: Source, Q, and Ground Motions

Abstract

We analyze an earthquake sequence which occurred 24 km NNW from Guadalajara Cathedral. The activity began on 15 December, 2015 with an Mw4.1 earthquake and resumed, again, on 11 May, 2016 when the largest earthquake of the sequence, Mw4.8, occurred. The earthquakes were recorded in the city by two accelerographs and at larger distances by broadband seismographs. The source region of the sequence is located in the north of the broad junction formed by NW-SE trending Tepic-Zacoalco rift, N-S trending Colima rift, and E-W trending Chapala rift. The focal mechanism of the largest event is characterized by: strike Ï• = 21º, dip δ= 49º, and rake λ= -86º, with horizontal tensional axis trending 110º. This mechanism is not consistent with NE-SW direction of motion measured on fault strike by Barrier et al. (1990) ~ 35 km WNW of Guadalajara. It also differs from the mechanism reported in a previous study for a seismic sequence in the Zacoalco rift about 60 km south of Guadalajara. Similarities among recorded waveforms at the accelerographic stations suggest that the mechanism of other events in the sequence were similar and the events were located in a small volume, probably 1 to 2 km in radius. From the analysis of the recordings of the 11 May shock along the Trans-Mexican Volcanic Belt, from Ceboruco volcano to the west and Popocatepetl volcano to the east, the attenuation parameter Q as 141f 0.63 was estimated. The earthquake on 11 May was felt very strongly in the city and produced peak ground acceleration (PGA) reaching 80 cm/s2. Relatively large earthquakes have been reported in the region; e.g., on 11 February, 1875 near the town of San Cristobal de la Barranca, about 40 km NNW of Guadalajara, therefore, the interest on using recordings from accelerographic stations to estimate peak ground motion parameters for scenario earthquakes of Mw≤ 6.0 using random vibration theory (RVT) and empirical Green’s function (EGF) techniques. From RVT simulations, the expected PGA, peak ground velocity (PGV), and peak ground displacement (PGD) at the accelerographic stations from an Mw6.0 earthquake in the source region of the sequence are 195 cm/s2, 10 cm/s, and 3 cm, respectively. The predictions from the EGF technique are somewhat higher but still within a factor of two of the RVT predictions.

A Source and Ground Motion Study of the Veracruz Earthquakes of 29 October 2009 (Mw5.7) and 4 August 2021 (Mw4.8): Evidence of Strong Azimuthal Variation of Attenuation

“…We take Q(f)=141f 0.63 estimated for the eastern and central Trans Mexican Volcanic Belt (Canas, 1986;Singh et al, 2017). β and ρ in the source region are assumed to be 3.75 km/s and 2.85 gm/cm 3 , respectively.…”

Ground motion simulations of the 1887 Pinal de Amoles (MW = 5.53) and the 1989 Landa de Matamoros (MW = 4.94) earthquakes, Querétaro, Mexico

“…The SBM method was tested and calibrated by simulating ground motions from the 11 May 2016 (M W = 4.8) Guadalajara earthquake. Singh et al (2017) studied source and ground motion characteristics from this event. To model this event, the results of Singh et al (2017) were considered as input parameters for the SBM: ρ = 2850 kg/m 3 , β = 3.8 km/s, L = 3.5 km, W = 3.5 km, V R = 3.7 km/s, κ = 0.01 s, and Q( f ) = 141f 0.63 .…”

“…Singh et al (2017) studied source and ground motion characteristics from this event. To model this event, the results of Singh et al (2017) were considered as input parameters for the SBM: ρ = 2850 kg/m 3 , β = 3.8 km/s, L = 3.5 km, W = 3.5 km, V R = 3.7 km/s, κ = 0.01 s, and Q( f ) = 141f 0.63 . D(r)= 1/r for r ≤ 70 km and 1/(70r) 0.5 for r > 70 km.…”

“…reported by Singh et al (2017). A spectral error function introduced by Castro et al (2008) was also used to calculate differences between observed and synthetic acceleration spectra (Figures 4 to 9).…”