Western Mexico seismic source model for the seismic hazard assessment of the Jalisco-Colima-Michoacán region

Abstract

The Mexican subduction zone, the Gulf of California spreading center, as well as the triple junction point around the Jalisco and the Michoacán Blocks, represents the most active seismogenic belts inducing seismic hazard in the Jalisco-Colima-Michoacán region. Herein, considering such seismotectonic setting, we develop a new seismic source model for the surrounding of Jalisco-Colima-Michoacán to be used as an input in the assessment of the seismic hazard of the region. This new model is based on revised Poissonian earthquake (1787–2018) and focal mechanism (1963–2015) catalogs, as well as crustal thickness data and all information about the geometry of the subducting slabs. The proposed model consists of a total of 37 area sources, comprising all the three different possible categories of seismicity: shallow crustal, interface subduction, and inslab earthquakes. A special care was taken during the delimitation of the boundaries for each area source to ensure that they represent a relatively homogeneous seismotectonic region and to include a relatively large number of earthquakes that enable us to compute as reliable as possible seismicity parameters. Although the sources were delimited following the standard criteria of assessing the probabilistic seismic hazard, they are also characterized in terms of their seismicity parameters (annual rate of earthquakes above Mw 4.0, b-value, and maximum expected magnitude), mean seismogenic depth, as well as the predominant stress regime. The proposed model defines and characterizes regionalized potential seismic sources that can contribute to the seismic hazard at the Jalisco-Colima-Michoacán region, providing the necessary information for seismic hazard estimates.

Appendices

Appendix I: Interface subduction-related seismogenic sources

1.1 SUB-01: Jalisco

This seismic source (SUB-01; Figs. 6, 7) includes the interface/interplate earthquake activity (an average depth of 20 km; Table 2) occurred due to the tectonic interaction between the Rivera Plate (to the southwest) and the North American Plate (to the northeast) (Figs. 1, 3, 6, 7). To the north and to the west from this defined zone, an abrupt change in both the seismicity and the faulting mechanisms is observed. This source underneath most of the coastal area of the state of Jalisco. Seismic activity rate in this region is relatively low, in comparison with those subsequent sources to the southeast. This low-occurrence seismic activity is greatly confirmed by the young age (about 10 My; Dewey and Suárez 1991) of the subducting plate and the slow subduction rates (< 2.0 cm/yr) (DeMets and Stein 1990; Suárez et al. 2013). This source (SUB-01; Figs. 6, 7) is compatible with the southeast portion of the SUB1 source (Fig. 2e) defined by Zúñiga et al. (2017). The November 22, 1837, Ms 7.7, the March 09, 1875, Ms 7.4, the January 20, 1900, Ms 7.6, the November 30, 1934, Ms 7.0, and the March 27, 1960 (Mw 6.0, ML 6.1) earthquakes represent examples for the largest reported events observed in this area source (see Table 1, Figs. 3, 6, 7).

1.2 SUB-02: Colima

This source (SUB-02; Figs. 6, 7) covers the interface/interplate earthquake activity (h ≤ 35 km, with an average depth of 11 km; Table 2) occurred due to the subduction of the northeastern portion of the Cocos Plate beneath the North American Plate (Figs. 1, 3, 6, 7). Geographically, this source is spanning all the coastal area of the Colima state, as well as some of the northwestern coast of the Michoacán state. Tectonically, it covers the seismic activity surrounding the Colima Rift. While Zúñiga et al. (2017) defined only one seismic source (SUB2; Fig. 2e) covering most of the subduction-related seismicity along the coastal area of Colima, Michoacán, Guerrero and western Oaxaca states, in the current model it has been preferred to subdivide this region into several sources (see Figs. 6, 7) depending on the characteristics of seismicity and the faulting style obtained from focal mechanism solutions (Fig. 7) and following the study by Pardo and Suárez (1995). This source (SUB-02; Figs. 6, 7) is compatible with the northwestern portion of the SUB2 source (Fig. 2e) delimited by Zúñiga et al. (2017). A relatively greater number of large earthquakes, in comparison to the previous defined source (SUB-01), has been observed in this one (SUB-02). The largest observed earthquakes within this area source are the March 25, 1806, Ms 7.5, the May 31, 1818, Ms 7.7, the June 22, 1932, Ms 7.0, the July 25, 1932, Ms 6.9, the June 29, 1935, Ms 6.9, the Jalisco-Colima tsunamigenic October 09, 1995 (Ms 7.3, Mw 8.0), and the January 22, 2003 (Ms 7.6, Mw 7.6) earthquakes (Table 1, Figs. 3, 6, 7).

1.3 SUB-03: Michoacán

As a continuation for the interface/interplate earthquake activity (h ≤ 35 km, with an average depth of 16 km; Table 2) occurred along the Mexican subduction zone (Figs. 3, 6, 7), this source (SUB-03; Figs. 6, 7) has been delimited to cover the seismicity along most of the coastal region of the state of Michoacán. Altogether with the previous seismic area source (SUB-02) and the subsequent ones (from SUB-04 to SUB-09), they are representing the subduction-related seismicity due to the interaction between the Cocos and the North American Plates (Figs. 1, 3, 6, 7). From the significant recorded earthquakes (Table 1, Figs. 3, 6, 7) within this seismic source, can be quoted the June 07, 1918, Ms 6.6, the January 30, 1973 (Ms 7.5, Mw 7.7), the June 30, 1973, Ms 7.5, the October 25, 1981 (Ms 7.3, Mw 7.2), the September 19, 1985 (Ms 8.1, Mw 8.1), and the January 11, 1997 (mb 6.5, ML 7.3) earthquakes. Among them, the September 19, 1985 (Ms 8.1, Mw 8.1) Michoacán earthquake represents a turning point in the seismic history of Mexico. This significant earthquake broke about 200 km along the Mexican subduction zone beneath the coast of Michoacán (e.g., Singh et al. 1988; Arciniega-Ceballos et al. 2018). It caused significant damages, reaching distances up to 300 km from its epicenter (e.g., Mexico City). A maximum horizontal acceleration value of 0.17 g was recorded at Mexico City, exceeding the limit of the seismic input of the building code in force (Anderson et al. 1986), as well as remarkable spectral amplifications (Singh et al. 1988). Official counting show that between 10,000 and 35,000 people died and/or missed, as well as more than 6,000 buildings were destroyed or seriously damaged (Arciniega-Ceballos et al. 2018).

1.4 SUB-04, SUB-05, and SUB-06: Guerrero

Guerrero region has been the goal of several recent seismic monitoring studies (e.g., Pacheco and Singh 2010), which allows researchers to better understanding the behavior and the geometry of the subduction zone specifically in this region. Two local seismic networks were in operation in the Guerrero region since about 1985. They are the Guerrero Accelerograph Array (Anderson et al. 1986), and the Guerrero Seismic Network (Suárez et al. 1990). Several researchers (e.g., Nishenko and Singh 1987b) have identified the coastal region of the state of Guerrero as a highly potential seismic zone for likely future earthquakes from the hypothesis of seismic gaps (Kelleher et al. 1973).

In the current work, three different seismic sources (SUB-04 “Guerrero Northwest”, SUB-05 “Guerrero Gap”, and SUB-06 “Guerrero Southeast”; Figs. 6, 7) have been delimited along the coast of the state of Guerrero, depending on the seismicity, the focal mechanisms characteristics (Figs. 3, 6, 7), as well as the geometry of the subducting slab (Fig. 4) and the crustal thickness (Fig. 5). While the seismic activity of the SUB-04 “Guerrero Northwest” source (an average depth of 20 km; Table 2 and Figs. 6, 7) is relatively similar to that exists in the previous one (SUB-03; Figs. 6, 7), it has been preferred to differentiate them because the geometry of the subducting slab along Guerrero (SUB-04; Figs. 6, 7) is completely different rather than Michoacán (SUB-03) (refer to Pardo and Suárez 1995; Pérez-Campos et al. 2008; Hayes et al. 2018). The largest observed/reported earthquakes (Table 1, Figs. 3, 6, 7) in this seismic source (SUB-04) are the March 27, 1908, Ms 7.0, the May 08, 1933, Ms 6.9, the February 22, 1943, Ms 7.7, the March 14, 1979 (Ms 7.6, Mw 7.4), the September 21, 1985 (Ms 7.6, Mw 7.5), and the April 18, 2014, Mw 7.3, events.

The second area source (SUB-05 “Guerrero Gap”; Figs. 6, 7) has been delimited specifically to cover the scattered seismicity (an average depth of 16 km; Table 2) along the so-called “Guerrero Gap” (Suárez et al. 1990). Although there is no reported significant recent seismicity, several historical and early instrumental earthquakes (Figs. 3, 6, 7) have been located in this region. The January 24, 1899, Ms 7.9, the January 28, 1934, Ms 6.8, the November 17, 1950, Ms 6.3, the May 31, 1990, Mw 6.0, and the April 13, 2007, Mw 6.0, earthquakes are from the largest reported ones here (Table 1).

The third area source (SUB-06 “Guerrero Southeast”; Figs. 6, 7) is characterized by a relative significant number of earthquakes with large magnitudes (an average depth of 17 km; Table 2) rather than the previous one (SUB-05; Figs. 6, 7). It covers the southeastern coastal region of the state of Guerrero. Historically, the April 07, 1845, Ms 7.9, the May 04, 1820, Ms 7.6, and the May 29, 1887, Ms 7.2, earthquakes are the largest reported ones (Table 1, Figs. 3, 6, 7). Moreover, since 1900, the April 15, 1907, Ms 7.7, the March 26, 1908, Ms 7.6, the July 28, 1957, Ms 7.7, and the April 25, 1989 (mb 6.2, Mw 6.9), earthquakes are from the most significant recorded events (Table 1, Figs. 3, 6, 7) in this source.

1.5 SUB-07: Guerrero-West Oaxaca

This area source (SUB-07; Figs. 6, 7) is located about 500 km far from the Jalisco and Colima states. It covers some of the coastal regions between the states of Guerrero and Oaxaca. It is characterized by the predominance of relatively large earthquakes (Figs. 3, 6, 7), both historical and instrumental (an average depth of 18 km; Table 2). Historically, the May 05, 1854, Ms 7.7, the December 02, 1890, Ms 7.2, the November 02, 1894, Ms 7.4, the August 04, 1928, Ms 7.4, and the August 17, 1929, Ms 7.0, earthquakes (Table 1, Figs. 3, 5) were the largest observed events. Moreover, in the instrumental period, several large earthquakes (Table 1, Figs. 3, 6) were also reported, e.g., the August 02, 1968, Ms 7.4, the September 14, 1995, Mw 7.3, the February 25, 1996, Mw 7.1, the March 20, 2012 (mb 6.5, Mw 7.5), and the February 16, 2018, Mw 7.3, events. Among them, while the May 05, 1854, Ms 7.7, earthquake is the largest recorded event, the February 16, 2018, Mw 7.3, earthquake (e.g., Li et al. 2020) is the most significant recent one in this area source.

1.6 SUB-08: South Oaxaca

This seismic source (SUB-08; Figs. 6, 7) is a continuation for the interface subduction-related earthquakes. It covers the southern coastal region of the state of Oaxaca. It is characterized by the occurrence of larger earthquakes (an average depth of 16 km; Table 2) relatively to the previously defined sources, along the Mexican subduction zone. The maximum reported magnitudes (Table 1) within the borders of this source correspond to the March 28, 1787, Mw 8.6 (Suárez and Albini 2009), the May 11, 1870, Ms 7.9, the June 17, 1928, Ms 8.0, the October 09, 1928, Ms 7.6, the November 29, 1978, (Ms 7.8, Mw 7.8), and the September 30, 1999 (mb 6.5, Mw 7.5), earthquakes, among others. The epicenter of the largest reported earthquake (the March 28, 1787, Mw 8.6 event) all over the seismic record in Mexico is situated within this seismic source. Suárez and Albini (2009) stated that this tsunamigenic earthquake occurring along the Mexican subduction zone had an estimated rupture length of about 450 km. A maximum felt intensity equals to VIII (MMI scale) was reported due to this earthquake (Suárez and Albini 2009).

1.7 SUB-09: Southeast Oaxaca

Due to the large distance (more than 500 km) between the seismicity occurred in this region (SUB-09; Figs. 3, 6, 7) and the Jalisco-Colima-Michoacán region, this will be the most distant considered source along the Mexican subduction zone (Fig. 1). Following the subdivision criteria of the Mexican subduction zone by Pardo and Suárez (1995), this source was defined to cover the subduction interface seismicity at the southeastern part of the state of Oaxaca (Figs. 6, 7). Still largest earthquakes occurred in this region (an average depth of 16 km; Table 2), with a focal mechanism style showing a mixed behavior. The June 05, 1897, Ms 7.4, the March 22, 1928, Ms 7.5, the August 23, 1965 (Ms 7.8, Mw 7.5), and the January 24, 1983 (mb 6.3, Mw 6.8) are the largest reported events in this zone (Table 1).

Appendix II: Inslab/intraplate seismogenic regions

2.1 IN-01: Jalisco-Colima inslab intermediate-depth

This area source (IN-01; Figs. 6, 7) covers the intermediate-depth seismicity (35 < h ≤ 75 km, with an average depth value of 53 km; Table 2), starting from the Middle American trench up to about 200 km horizontal distance, beneath the states of Jalisco and Colima, as well as the western part of Michoacán. Together with the subsequent intermediate-depth coastal area sources (IN-02, IN-03, IN-04, and IN-05; Figs. 6, 7), they represent a transitional volumetric region between the subduction-related seismicity (SUB-sources) and the deeper inslab one (IND-sources). Within this seismic source (IN-01), only three focal mechanisms are available, corresponding to the January 26, 1974 (mb 5.2, Mw 5.6), the March 9, 1981, mb 5.7, and the August 15, 1999 (Ms 5.2, Mw 5.2) earthquakes. They are exhibiting normal-faulting with strike-slip component, thrust-faulting, and normal-faulting mechanisms, respectively (Fig. 7). On the other hand, the largest observed earthquakes (Table 1, Fig. 6) within this source are the June 07, 1911, Ms 7.7, the April 26, 1968 (Ms 6.3, Mw 6.1), the October 18, 1973 (mb 6.0, Ms 6.8), the March 09, 1981, mb 5.7, and the February 09, 2018, Mw 6.0, earthquakes.

2.2 IN-02: Michoacán-Guerrero coastal inslab intermediate-depth

For about 450 km-distance parallel to the Middle American trench (Fig. 1), and about 120 km-distance perpendicular to it, a second seismic source (IN-02; Figs. 6, 7) has been delimited beneath the states border of Michoacán and Guerrero to cover the intermediate-depth inslab seismicity (an average depth of 45 km; Table 2). Faulting mechanism (Fig. 7) is similar to the previous IN-01 source; mostly earthquakes exhibit thrust-faulting mechanisms, except some of them that show a normal-faulting style. Examples for the largest reported earthquakes (Table 1, Figs. 3, 6, 7) within this area source are the July 30, 1909, Ms 7.3, the December 16, 1911, Ms 7.6, the May 11, 1962, Ms 7.2, the July 02, 1968, Ms 6.7, the January 26, 1979 (Ms 6.9, Mw 6.6), and the December 10, 1994 (Ms 6.6, Mw 6.5) events.

2.3 IN-03: Guerrero-Oaxaca coastal inslab intermediate-depth

Along the Guerrero-Oaxaca coastal boundary, and parallel to the Middle American trench (Fig. 1), this area source (IN-03; Figs. 6, 7) has been defined to depict the inslab intermediate-depth seismicity (an average depth of 48 km; Table 2 and Fig. 6), which mainly shows thrust-faulting mechanisms. The largest observed events (Table 1, Figs. 3, 6, 7) inside this zone are the December 21, 1965, mb 5.2, the July 18, 1974, mb 5.6, the July 02, 1984 (mb 5.9, Mw 6.4), the June 07, 1987, mb 5.5, and the June 07, 1992, mb 5.3, earthquakes.

2.4 IN-04: Southern Oaxaca inslab intermediate-depth

As in-depth continuation for the previously defined subduction area source (SUB-08; Figs. 6, 7), and as a lateral extension of the inslab intermediate-depth sources (IN-01, IN-02, and IN-03) parallel to the Middle American trench, this area source (IN-04; Figs. 6, 7) has been defined. This seismic source covers the intermediate-depth inslab seismicity (35 < h ≤ 75 km, with an average depth of 55 km; Table 2) that occur beneath southern Oaxaca. Seismicity show a mixed style of faulting mechanisms, normal and thrust faulting, which considered as a transitional area between the thrust-faulting subduction interface seismicity (for SUB-sources) and the deeper normal-faulting intraslab seismicity (IND-sources). The maximum observed earthquakes in this seismic zone are the January 15, 1931, Ms 7.8, the May 13, 1954, Mw 6.3, the December 13, 1984, mb 5.4, the August 19, 2006, Ms 5.4, and the February 08, 2010, ML 5.8, events, among others (Table 1).

2.5 IN-05: Oaxaca-Chiapas inslab intermediate-depth

Another seismic source (IN-05; Figs. 6, 7) has been defined to cover the inslab intermediate-depth seismicity (an average depth of 55 km; Table 2) located beneath the border between the states of Oaxaca and Chiapas. This source is an extension in depth of the last considered subduction zone (SUB-09; Figs. 6, 7). The largest reported earthquakes within this seismic source are the June 07, 1946, Ms 6.9, the April 22, 1962, Ms 6.0, the April 06, 1992, MD 6.4, the August 18, 2004, mb 5.7, the January 21, 2012 (mb 5.9, Mw 6.2), and the September 08, 2017 (Ms 8.2, Mw 8.2) events (Table 1). Few focal mechanism solutions are available in this source, which mainly shows a mixed normal- and thrust-faulting mechanisms (Fig. 7). Among the largest Mexican earthquakes, the most recent and largest instrumental one, the September 08, 2017 (Ms 8.2, Mw 8.2) Chiapas earthquake, is located here. This earthquake is the largest reported one in Chiapas since 1902 (Ramírez-Herrera et al. 2018). There were more than 100 fatalities, huge damage all over the states of Chiapas, Oaxaca, and Tabasco, and about 41,000 buildings were damaged in Chiapas only; more than 1.5 million people were somehow affected by this earthquake. This intraplate normal-faulting event, occurred on the oceanic subducting plate, generated a tsunami that was recorded at many tide gauges in Mexico and the Pacific Ocean (Ramírez-Herrera et al. 2018).

2.6 IN-06: Michoacán-Guerrero inslab intermediate-depth

However, the previously defined sources (from IN-01 to IN-05) are exhibiting a clear mixed style of faulting, the subsequent ones (from IN-06 to IN-09) are showing a normal-faulting mechanism as the most dominant style (Fig. 7). At a horizontal distance of about 120 km far from the trench, another seismic source (IN-06; Figs. 6, 7) has been delimited to delineate the inslab intermediate-depth (35 < h ≤ 75 km, with an average depth value of 62 km; Table 2) earthquakes exhibiting mostly normal-faulting mechanism solutions (Fig. 7). The maximum observed magnitudes (Table 1, Figs. 3, 6) within this source correspond to the July 05, 1978, mb 5.6, the May 23, 1994 (mb 5.9, Mw 6.3), the December 29, 1999, mb 5.9, the August 11, 2006 (mb 6.0, Mw 6.1), the December 11, 2011 (mb 6.1, Mw 6.5), and the November 15, 2012 (Mw 6.1, ML 6.1) earthquakes, among others.

2.7 IN-07: Guerrero-Puebla-Oaxaca inslab intermediate-depth

As a lateral continuation of the previous seismic source (IN-06; Figs. 6, 7), and to cover the inslab intermediate-depth earthquakes (an average depth of 57 km; Table 2) beneath the common border between the states of Guerrero, Puebla, and Oaxaca, this area source (IN-07; Figs. 6, 7) is proposed. The focal mechanism characterization (Fig. 7) of this source is similar to the previous one. From the largest reported earthquakes (Table 1, Figs. 3, 6, 7) within this source, the October 24, 1980 (mb 6.4, Ms 7.0), the July 21, 2000, ML 6.0, the May 22, 2009, mb 5.8, the June 16, 2013, Mw 5.9, and the September 19, 2017 (Mw 7.1, ML 7.1) events can be cited. One of the most recent and destructive earthquakes in the seismic record of Mexico is the September 19, 2017 (Mw 7.1, ML 7.1) Morelos-Puebla intraslab earthquake, which occurred 32 years after the well-known September 19, 1985 (Ms 8.1, Mw 8.1) Michoacán earthquake. The September 19, 2017 earthquake had a depth of 57 km and a hypocentral distance of about 127 km from Mexico City (Singh et al. 2018). Several towns and villages in the epicentral area of the earthquake were destroyed. A total of 369 persons died in Mexico City (228), Morelos (74) and Puebla (45). In addition, 44 buildings collapsed, and about 600 buildings were damaged in Mexico City (Singh et al. 2018).

2.8 IN-08: Northern Oaxaca inslab intermediate-depth

This seismic source (IN-08; Figs. 6, 7) represents a lateral extension of the previously considered one (IN-07). Moderate-magnitude inslab intermediate-depth earthquakes (an average depth of 65 km; Table 2) are located in this source. The September 07, 1983, mb 5.3, the September 15, 1985 (mb 6.0, Mw 6.0), the February 23, 1994, mb 5.6, the August 28, 1994, mb 5.5, and the June 15, 1999 (mb 6.4, Mw 6.9) earthquakes are the largest reported ones (Table 1). All the available focal mechanisms exhibit a normal-faulting mechanism (Fig. 7).

2.9 IN-09: Oaxaca-Veracruz inslab intermediate-depth

This source (IN-09; Figs. 6, 7) is the last and most distant one defined for the intermediate-depth inslab seismicity (an average depth of 52 km; Table 2). This is due to the large distance between seismicity in this area source and the region of interest. This area source covers intermediate-depth intraplate seismicity (35 < h ≤ 75 km) occurring beneath the eastern border between the states of Oaxaca and Veracruz. Moderate-magnitude earthquakes are reported to be occurred here. For instance, the July 11, 1946, Mw 7.1, the September 17, 1967, mb 5.3, the October 20, 1969, mb 5.4, and the July 29, 1985, mb 5.3, earthquakes (Table 1). Only one focal mechanism solution is available inside this area source, which corresponds to the January 06, 2013, Ms 5.3 earthquake, showing a strike-slip faulting mechanism (Fig. 7).

2.10 IND-01: Jalisco-Colima-Michoacán inslab deep

This source (IND-01; Figs. 6, 7) defines the inslab deeper seismicity (> 75 km, with an average depth of 100 km; Table 2) occurring far from the Middle American trench (Fig. 1), beneath the states of Jalisco, Colima and Michoacán, due to the subducting slabs. This zone is characterized by few scattered low- to moderate-magnitude earthquakes (Figs. 3, 6, 7). The largest reported events within this region were the July 29, 1973, mb 5.1, the October 21, 1976, mb 4.7, the January 19, 1988, mb 5.3, the September 29, 1992, mb 5.0, and the August 15, 1999, Mw 5.3, earthquakes. Only two focal mechanism solutions (Fig. 7) exhibiting normal-faulting mechanisms are available. They are related to the July 29, 1973, mb 5.0, and the September 29, 1992, Ms 5.3, earthquakes (Table 1).

2.11 IND-02: Michoacán-Guerrero inslab deep

As a lateral continuation of the previous source (IND-01; Figs. 6, 7), and beneath the continental border between Michoacán and Guerrero states, this second source (IND-02; Figs. 6, 7) delimits the deeper inslab seismicity (mean depth value of 98 km; Table 2 and Figs. 3, 6, 7), mostly exhibiting normal-faulting mechanisms (Fig. 7). It is considered as an extension in depth of the IN-06 inslab intermediate-depth seismic source (Figs. 6, 7). In contrast to the previously mentioned seismic source (IND-01), this one shows large earthquakes, both historical and instrumental (Table 1, Figs. 3, 6, 7), for instance, the June 19, 1858, Ms 7.5, the June 28, 1938, Ms 6.5, the June 20, 1942, Ms 6.7, the April 21, 1945, Ms 6.5, the July 06, 1964 (mb 6.5, Mw 7.3), and the May 22, 1997, Mw 6.5, events (Table 1).

2.12 IND-03: Guerrero-Puebla-Oaxaca inslab deep

Same as in the IN-07 inslab intermediate-depth seismic source (Figs. 6, 7), and as a continuation in depth to that source, this inslab deeper seismic source (IND-03 with an average depth of 95 km; Table 2 and Figs. 6, 7) has been proposed. It is situated in depth beneath the common border between the states of Guerrero, Puebla and Oaxaca. No focal mechanism solutions were available within this zone. From the largest observed earthquakes occurred in this seismic source (Table 1, Figs. 3, 6, 7) can be cited the March 16, 1874, Ms 7.3, the May 17, 1879, Ms 7.0, the July 19, 1882, Ms 7.5, the February 03, 1911, Ms 7.2, and the January 06, 1948, Ms 7.0, earthquakes (Table 1).

2.13 IND-04: Puebla-Veracruz-Oaxaca inslab deep

This source (IND-04; Figs. 6, 7) delimits the inslab deep seismicity (an average depth of 92 km; Table 2) occurring along the subducting slab. It covers the geographical area, in depth (> 75 km), which defines the common borders between the states of Puebla, Veracruz and Oaxaca. It is an in-depth extension for the previously defined IN-08 inslab intermediate-depth seismic source. Large earthquakes were reported to be occurred within this defined seismic source (Figs. 6, 7). They are the October 03, 1864, Ms 7.3, the September 24, 1910, Ms 6.9, the July 26, 1937, Ms 7.2, the December 12, 1951, Ms 7.0, the May 24, 1959, Ms 6.8, and the August 28, 1973 (mb 6.6, Ms 7.3) earthquakes, among others (Table 1). Only one focal mechanism solution is available in this source, exhibiting a normal-faulting mechanism, corresponding to the August 28, 1973 (mb 6.6, Ms 7.3) earthquake.

2.14 IND-05: Veracruz-Oaxaca inslab deep

At about 500 km far away, as a conservative distance, from the boundaries of the Michoacán State, a final inslab deep seismic source (IND-05; Figs. 6, 7) was defined to cover the seismicity (an average depth of 120 km; Table 2) that occurred in depth beneath the eastern border between the states of Veracruz and Oaxaca. It is considered an extension in depth for the intraplate seismicity defined in the IN-09 inslab intermediate-depth seismic source (Figs. 6, 7). From the largest observed earthquakes within this source are the June 02, 1916, Ms 7.0, the July 13, 1960 (Ms 6.9, ML 6.9), the June 22, 1979 (mb 6.5, Mw 6.9), the October 21, 1995 (Mw 7.2, ML 7.1), the February 12, 2008 (mb 5.9, Mw 6.5), and the April 07, 2011 (Mw 6.7, ML 6.7) events (Table 1). Several focal mechanism solutions are available in this source, most of them showing a normal- and strike-slip faulting mechanisms.

Appendix III: Shallow crustal seismogenic sources

3.1 SC-01: Gulf of California

This seismic source (SC-01; Figs. 6, 7) delimits the shallow crustal seismicity (an average depth of 17 km; Table 2) in the Gulf of California occurred along the transform boundary between the Pacific Plate (toward the west) and the North American Plate (toward the east). Fault-plane solutions for earthquakes occurred within this area source show a mixed mode of faulting, resulting from the stresses produced by the interaction between both plates. Most of the earthquakes show a strike-slip faulting regime, although some of them shows normal-faulting mechanisms (Fig. 7). This depends whether they occurred along the transform plate boundary (the first case), or along the spreading ridges (the second one) (Doser 1992; Thatcher 1972). The largest observed earthquakes (Table 1; Figs. 3, 6) included in this seismic source are the March 05, 1901, Ms 7.2, the December 09, 1901, Ms 7.5, the May 23, 1918, Ms 6.8, the August 28, 1923, Mw 6.8, the June 27, 1945, Ms 6.8, the October 21, 2010 (mb 6.1, Ms 6.9, Mw 6.7), and the September 13, 2015 (ML 6.7, Mw 6.7) earthquakes.

3.2 SC-02: Pacific-Rivera Ridge

This area source (SC-02; Figs. 6, 7) includes the shallow seismicity (mean depth value of 17 km; Table 2) included along the divergent spreading boundary (Pacific-Rivera Ridge, Fig. 1), between the Pacific Plate (to the northwest) and the Rivera Plate (to the southeast). Fault-plane solutions (Fig. 7) show mixed faulting mechanisms: normal-faulting, strike-slip faulting with normal component, and strike-slip faulting mechanisms. Examples of large earthquakes (Table 1; Figs. 3, 6, 7) that have been reported to be occurred within this seismic source are the May 09, 1946, Mw 6.3, the September 30, 1953, Ms 6.8, the February 17, 1984, Mw 6.1, the November 13, 2001, Mw 6.1, and the May 08, 2005, Ms 6.1 earthquakes.

3.3 SC-03: Transition between the Gulf of California and the Subduction zone

Since there are no structural, morphologic nor seismic evidences that could confirm the continuation of the Gulf of California (SC-01) transform boundary to the Jalisco Block (Dañobeitia et al. 2016), and to delimit the scattered seismicity (mean depth value of 16 km; Table 2) along this transition area, this area source (SC-03; Figs. 6, 7) has been defined. This source is bordered by El Gordo Graben from the east and the near aseismic part of the Rivera Plate from the west (Fig. 1). It covers the seismicity surrounding the Tres Marías Islands, to the north (Figs. 1, 3, 6, 7), approaching the Mexican subduction zone (SUB-01) to the south. The May 11, 1926 (Ms 6.2, Mw 6.2), the December 04, 1948, Ms 6.9, the August 12, 1971, mb 5.6, and the February 09, 1976, mb 5.6 earthquakes represent the largest recorded events within this zone (Table 1; Figs. 3, 6).

3.4 SC-04: Rivera transform fault

This seismic source (SC-04; Figs. 3, 6) corresponds to the shallow seismicity (mean depth value of 16 km; Table 2) due to the Rivera Transform Fault (Fig. 1), delimiting the southwestern border between the Rivera and the Pacific Plates. Mostly earthquakes show strike-slip faulting mechanisms (Fig. 7). Several large earthquakes were documented (Table 1; Figs. 3, 6, 7) to be occurred within this source. Examples for the largest reported events are the January 14, 1899, Ms 7.4, the April 10, 1906, Ms 7.2, the November 16, 1925, Ms 7.0, the December 06, 1965 (Ms 6.1, Mw 6.7), the October 20, 1972 (Ms 6.4, Mw 6.7), the May 01, 1997 (mb 6.1, Mw 6.9), and the January 21, 2016, Mw 6.6, earthquakes. One of the largest tsunamis that was reported during the twentieth century at the Port of Zihuatanejo, Guerrero, was related to the November 16, 1925, Ms 7.0, earthquake (Singh et al. 1998). In spite of the earthquake’s epicenter that was located 600 km far from the Port of Zihuatanejo, a high tsunami of about 6 to 9 m was reported (Sánchez and Farreras 1993; Farreras 1997).

3.5 SC-05: Rivera-Cocos-Pacific Junction

This seismic source (SC-05; Figs. 6, 7) was delimited including areas from the Middle American Trench (to the north) southward along the border between the Rivera (to the northwest), the Cocos (to the southeast), and the Pacific (to the southwest) Plates. This is to cover the seismicity (an average depth of 16 km; Table 2 and Figs. 3, 6, 7) in this common border between the surrounding tectonic plates. The largest reported events (Table 1; Figs. 3, 6, 7) within this area source are the December 22, 1937, Ms 6.5, the August 29, 1989 (mb 5.7, Ms 6.6), the May 19, 2001, ML 6.5, and the September 23, 2008, ML 6.4, earthquakes. Most of the seismicity exhibits strike-slip faulting mechanisms (Fig. 7), with some of them showing a normal-faulting behavior.

3.6 SC-06: Pacific-Cocos Rise

Even when this seismic source (SC-06; Figs. 6, 7) defines a relatively distant shallow seismicity (mean depth value of 13 km; Table 2) along the Pacific-Cocos Rise (Fig. 1), it was delimited because its related seismicity could contribute to some extent to the seismic hazard at the Jalisco-Colima-Michoacán region. Moderate seismic activity (Figs. 3, 6, 7) was observed along this region. The largest observed earthquakes (Table 1) are the January 25, 1931, Ms 6.0, the January 20, 1955, Mw 6.0, the October 22, 1978 (mb 5.1, Mw 5.7), the October 28, 1994 (mb 5.3, Mw 5.9), the January 22, 2011, Ms 5.5, and the July 23, 2016, mb 5.5, events. Although this source defines the divergence between the Cocos (to the east) and the Pacific (to the west) Plates, most of the available focal mechanism solutions (Fig. 7) show a strike-slip style of faulting.

3.7 SC-07 and SC-08: Outer-Rise earthquakes

A few scattered but significant seismicity (Figs. 3, 6, 7) characterizes these delimited seismic sources (SC-07 and SC-08; Figs. 6, 7). The involved area extends parallel to the Mexican subduction zone and the Middle American trench (Fig. 1). They were defined to delimit the so-called outer-rise earthquakes taken place to the west of the trench up to an average horizontal distance of 100 km (Figs. 6, 7). The seismicity within this region is preferred to be differentiated into two different sources (SC-07 and SC-08, with mean depth values of 16 and 19 km, respectively; Table 2), depending on the seismicity, the characteristics of the trench, as well as the proximity (as SC-07) or the remoteness (as SC-08) in relation to the region of interest. The largest observed events (Table 1; Figs. 3, 6, 7) within the source SC-07 are the January 14, 1903, Ms 7.7, the April 10, 1957, Ms 6.2, the February 04, 1970, (Ms 6.6, Mw 6.4), the December 16, 1997, ML 6.0, and the April 18, 2002, Mw 6.7, earthquakes. While, in the source SC-08, the December 29, 1917, Ms 7.1, the December 29, 1936, Ms 6.3, the October 28, 1942, Ms 6.2, the September 30, 1993 (mb 5.6, Mw 6.5), the July 04, 1994 (mb 6.1, Mw 6.5), the May 05, 1999 (mb 5.9, Mw 6.3), and the August 13, 2011, Ms 6.3, earthquakes are examples for the largest reported events. Few focal mechanism solutions (Fig. 7) are available for both sources.

3.8 SC-09: Sierra Madre Occidental

This area source (SC-09; Figs. 6, 7) is compatible to a great extent with the Sierra Madre Occidental (SMO) source (Fig. 2e) defined by Zúñiga et al. (2017). In the proposed delimitation, it includes the shallow seismicity (mean depth value of 13 km; Table 2) beneath most of Sinaloa state and the western portion of Durango state (Figs. 6, 7). It is characterized by low-to-moderate-magnitude scarce earthquakes. The largest reported events (Figs. 3, 6, 7) within this seismic source are the May 10, 1930, Mw 5.9, the October 02, 1988, mb 4.9, and the September 05, 2011, Ms 4.8, earthquakes. Only one focal mechanism solution (Fig. 7) is available within this source, corresponding to the July 12, 2009, Ms 4.6, earthquake, reflecting a normal-faulting mechanism.

3.9 SC-10: Durango-Zacatecas

This proposed seismic source (SC-10; Figs. 6, 7) includes the scattered shallow seismicity (mean depth value of 7 km; Table 2 and Figs. 3, 6, 7) occurring within the shallow crust of Durango and Zacatecas states, as well as the southern Sinaloa state (to the west), Aguascalientes and Nayarit states (to the south) and Coahuila (to the northeast) (Figs. 6, 7). It roughly covers the southern section of the previously defined SMO and BAR sources (Fig. 2e) proposed by Zúñiga et al. (2017). A few seismicity (Figs. 6) has been reported within this relatively stable region (included in the North American Plate), with the exception of the November 01, 1928, Mw 6.5, Durango earthquake that lies to the north from this source. The largest observed earthquakes (Figs. 3, 6, 7) within this area source are the May 31, 1995, mb 4.8, and the August 01, 2007, Ms 4.4, events. No focal mechanism solutions are available in this area source.

3.10 SC-11: Burgos Basin

Toward the northeastern portion of Mexico, and to the west of the Gulf of Mexico (Figs. 6, 7), another seismic source (SC-11) has been delimited to cover the low-to-moderate-magnitude earthquakes (mean depth value of 8 km; Table 2 and Figs. 3, 6) occurred within the Burgos Basin in the states of Nuevo León and San Luis Potosí, as well as some areas of the states of Coahuila (to the northwest), Zacatecas (to the west), and Guanajuato and Querétaro (to the south) (Figs. 6, 7). This area source overlaps with the BB seismic zone (Fig. 2e) defined by Zúñiga et al. (2017). The largest reported events are the February 26, 1986, mb 4.8, the September 10, 1989, Ms 4.4, and the November 26, 2013, Ms 4.3, earthquakes. No focal mechanism solutions are available within this source. However, Suter (1987), based on borehole elongation data, proposed a NW–SE trend for the minimum stress axis in this region. Moreover, a slight N-S alignment of low-magnitude earthquake epicenters recorded in the last years is observable (Zúñiga et al. 2017).

3.11 SC-12: Trans-Mexican Volcanic Belt

This proposed seismic source (SC-12; Figs. 6, 7) includes scattered moderate-magnitude earthquakes (an average depth value of 14 km; Table 2 and Figs. 3, 6, 7) occurring along the TMVB (Fig. 1) crossing Mexico, starting from the Pacific coast (to the west) and ending with the coast of the Gulf of Mexico (to the east). This seismic source is situated below the highly populated regions along the TMVB: southern Nayarit, Jalisco, southern Guanajuato, northern Michoacán, southern Querétaro, Hidalgo, Ciudad de Mexico, Morelos, Tlaxcala, Puebla, and Veracruz (Figs. 6, 7). This source is of utmost importance from the seismic hazard point of view due to the higher population density within these previously mentioned states. In the past, due to the shallower depths of the earthquakes and their proximity to the densely populated cities along the TMVB, some moderate- to high-size earthquakes (Table 1; Figs. 3, 6, 7) were turned catastrophic. For instance, the February 11, 1875, Ms 7.5, earthquake that occurred close to the city of Guadalajara, caused a remarkable damage in Guadalajara and the neighboring cities (Suárez and Caballero-Jiménez 2012). Another largely famous example was the November 19, 1912, Ms 6.9, Acambay earthquake that occurred within the Acambay Graben. This graben has been the subject of further paleoseismological studies (e.g., Langridge et al. 2000, 2013; Ortuño et al. 2019) concluding that a significant earthquake is expected within this region every 300–600 years. From a seismicity point of view (Table 1; Figs. 3, 6, 7), some of the largest reported earthquakes within this defined seismic source are the February 11, 1875, Ms 7.5, the November 19, 1912, Ms 6.9, the June 03, 1932, Ms 8.2, the June 18, 1932, Ms 7.8, the April 15, 1941, Ms 7.7, the October 03, 1947, Ms 7.0, the June 04, 1960, Ms 6.4, and the May 08, 2016, mb 5.8, events. A few focal mechanism solutions (Fig. 7) are available in this area source, most of them indicating a normal-faulting mechanism with some left-lateral strike-slip component.

3.12 SC-13: Tuxtla volcanic field

This seismic source (SC-13; Figs. 6, 7) incorporates the shallow crustal seismicity (mean depth value of 17 km; Table 2) within the Tuxtla Volcanic Field. This volcanic field, also known as Los Tuxtlas Field, is an isolated basaltic volcanic area that emerges from the lowlands of the western border of the Gulf of Mexico (Espindola et al. 2016). Due to its remoteness from the TMVB, it was preferred to define a separate seismic source including this seismicity that might be related to some extent to the volcanic activity. Few moderate earthquakes are observed within this seismic source (Figs. 6, 7). The August 26, 1959, Ms 6.4, the March 11, 1967, Mw 5.9, and the October 29, 2009, Mw 5.7, earthquakes depict the largest reported events in this seismic source. Only one focal mechanism solution (the October 29, 2009, Mw 5.7, earthquake) is available within the limits of this source, exhibiting a thrust-faulting mechanism (Fig. 7).

3.13 SC-14: Guerrero-Puebla

This area source (SC-14; Figs. 6, 7) was delimited to include the shallow-depth moderate-seismic activity (an average depth value of 34 km; Table 2 and Figs. 3, 6) to the south of the TMVB. It mostly consists of the shallow crustal activity occurred beneath the Guerrero-Oaxaca border as well as in southern Puebla (Figs. 6, 7). This seismic source is compatible with the northern portion of the NAM zone (Fig. 2e) proposed by Zúñiga et al. (2017). The January 16, 1902, Ms 7.0, the November 21, 1916, Ms 6.8, the October 19, 1917, Ms 6.3, the December 23, 1937, Ms 7.5, and the December 14, 1950, Ms 7.3, events are the largest recorded earthquakes (Table 1, Figs. 3, 6, 7) within this source. Only one fault-plane solution (Fig. 7) is reported in this zone, related to the October 29, 2001, Ms 5.0, earthquake, exhibiting a normal-faulting mechanism.