## 1 Introduction  
Western Mexico is a complex tectonic setting that involves subduction, volcanism, and continental rifting. In this region, the oceanic Rivera and Cocos plates subduct beneath the continental North American plate (Figure 1), causing continental rifting [1, 2], unusual volcanism [3], and tearing of the subducting slabs [4]. The Rivera plate is separated from the Cocos plate about 7-10 Ma, and both oceanic plates move with different relative velocities with regarding North America plate [5]. Although the Rivera and Cocos slabs are well separated at depths below 150 km, the surface boundary is fuzzy [4]. Seismicity studies show different dip angles for the subducting Rivera plates (\(\sim\)37\({}^{\circ}\)) and Cocos (\(\sim\)30\({}^{\circ}\)) plates near the Colima rift [6]. There is also evidence that the Rivera subducting plate has been re-subducted [7] and a clear gap between the Rivera and Cocos plates is present at depths below 150 km [4]. Above the tip of this gap lies the Colima volcano in the Colima rift. Since the Colima rift and its offshore extension, El Gordo Graben, is an active tectonic feature, seismicity along its boundaries is recurrent. Although the region is an active subduction zone, the presence of the Colima rift may induce large strike-slip earthquakes. The Jalisco and Michoacan blocks are separated by the Colima rift (CR). The Colima rift has been explained as passive rifting caused by the differential motion between the Rivera and Cocos slabs and their coupling with the dominant plate [8; 9]. Active rifting of the CR as a consequence of the relocation of the East Pacific Rise has also been suggested [1; 2]. The authors in [10] proposed the existence of a mantle plume as an alternative explanation for CR. A southeastern motion of the Michoacan block with respect to the North American plate has also been suggested to explain the CR [5; 11]. In this work, the possible effects of a strike-slip earthquake nucleated in the region of the Colima rift on the Michoacan block are evaluated. Five main geological provinces have been identified in Michoacan [12]: the Sierra Madre del Sur, the Topalcatepec Depression, the Balsas Depression, the Michoacan and Guanajuato Volcanic Field, and the Bajio Michoacano (Figure 2). The Sierra Madre del Sur is composed of volcanic sedimentary sequences of the Guerrero terrain. These sequences are controlled by N-S and NO-SE structures and large magmatic bodies of 50 Ma. The NO-SE Topalcatepec Depression presents Quaternary and Tertiary volcanic rock formations and Cretacic volcanic igneous and sedimentary rocks in Infiermillo dam. The Balsas Depression was formed by rock structures of the Guerrero terrain and has the influence of two large fault systems in the Guerrero-Michoacan limits. The Michoacan-Guanajuato Volcanic Field is composed of monogenetic volcanism and the felsic magmatism islands of Patamban, Tzirate, and Cerro la Nieve. The Bajio Michoacano is located in the northern part of Michoacan and has developed large lake basins by faulting or volcanic processes. This region is controlled by the E-O and NE-SO Morelia-Acambay fault system. These five geological provinces are controlled by morphobtructural regions driven by fault systems related to the stress field [13]. Figure 1: Tectonic setting of western Mexico. RP = Rivera Plate, JB = Jalisco Block, MB = Michoacan Block, G = El Gordo Graben, CV = Colima Volcano, TMVB = Trans Mexican Volcanic Belt, MAT = Middle America Trench. Dots inside the TMVB stand for volcanic fields. Although the tectonic features that generate the most prominent earthquakes in the state of Michoacan are defined by thrust fault earthquakes produced by subduction, there have been occurrences of lateral fault earthquakes produced in the Colima rift (CR) [14]. The CR region, in the Colima-Michoacan limits, has been a zone of important seismicity. The Tecoman earthquake on 21 January 2003 (M = 7.4) is the largest seismic event of the present century [15].