Empirical models to estimate horizontal Fourier acceleration spectra from earthquakes in Northern Gulf of California, Mexico

Modelos empíricos para estimar los espectros de aceleración de Fourier horizontal a partir de terremotos en el norte del Golfo de California, México

José Sequeira-Arguedas1    , Raúl R. Castro1

1 Departamento de Sismología, División Ciencias de la Tierra, Centro de Investigación y de Educación Superior de Ensenada, Baja California, México (CICESE). Carretera Ensenada-Tijuana 3918, Zona Playitas, 22860, Ensenada, Baja California, México.

* Corresponding author: 

(R. R. Castro) This email address is being protected from spambots. You need JavaScript enabled to view it.

How to cite this article:

Sequeira-Arguedas J., & Castro, R. R. (2026). Empirical models to estimate horizontal Fourier acceleration spectra from earthquakes in Northern Gulf of California, Mexico: Boletín de la Sociedad Geológica Mexicana, 78(2), A051125. https://doi.org/10.18268/BSGM2026v78n2A051125

Manuscript received: June 26, 2025. Corrected manuscript received: October 15, 2025. Manuscript accepted: October 27, 2025.

ABSTRACT

We propose two empirical predictive equations to estimate acceleration spectra at rock sites using epicentral distance and moment magnitude as input parameters, in the frequency range of 0.32 to 25.12 Hz. We considered 42 earthquakes located in the northern region (29.5°N to 31.7°N) of the Gulf of California (GoC) that occurred in the period 2015-2022 with magnitudes between 4.0 to 5.7 Mw. We compiled 180 acceleration records from eight stations of the Broadband Seismological Network of the Gulf of California and the Northwestern Mexico Seismological Network, operated by CICESE. We calculated the horizontal acceleration spectra selecting time windows with variable length according to epicentral distance. We consider two models, one linear and another quadratic for the magnitude, obtaining the regression coefficients through ordinary least squares. The linear model was found to be more appropriate for the region, as the quadratic model yielded physically unlikely results at low frequencies. Comparative analysis with  ground  motion  models  from other tectonic regions highlighted the relevance of our regional approach. Additionally, a scenario for a Mw 5.3 event was simulated to evaluate the performance of the linear model in predicting spectral amplitudes in rock. Both models are considered a mean regional attenuation value and give reliable amplitudes at low frequencies (f ≤ 10 Hz); therefore, their applicability across epicentral distances must be carefully used on prior knowledge of the site amplification function. It was also evident the fitting difference of Fourier acceleration spectra between the northern (above 29.5° of latitude) and central GoC (Canal de Ballenas region), possibly attributed to azimuthal coverage, geological heterogeneities, rock quality and different states of stress.

Keywords:  empirical  spectral models, Gulf of California, horizontal Fourier acceleration spectrum, data inversion.