The Impact of the Chiapas Tsunami of 8 September 2017 on the Coast of Mexico. Part 1: Observations, Statistics, and Energy Partitioning

Abstract

The major (M w 8.2) intraplate normal-fault earthquake of 8 September 2017 in the Gulf of Tehuantepec (Chiapas, Mexico) generated a strong tsunami that severely impacted the nearby coasts of Mexico and Central America. Tsunami waves in the near-field area were measured by seventeen high-resolution coastal tide gauges and by three open-ocean DART stations anchored offshore from the affected region. Data from these sites, together with those from four distant DARTs, were used for comprehensive analyses of the 2017 event. De-tided sea level time series were examined to determine the statistical and spectral characteristics of the 2017 tsunami waves along the Mexican and Central American coastline. The characteristics of the recorded waves from this near-field event were compared with those from two great far-field events: the 2010 Chile and the 2011 Tohoku tsunamis. Maximum trough-to-crest wave heights for the 2017 tsunami were recorded at Puerto Chiapas (351 cm), Salina Cruz (209 cm), Acapulco (160 cm), Huatulco (137 cm) and Acajutla, El Salvador (118 cm). While maximum 2010 and 2011 tsunami waves were observed at specific ''hot spots'' (sites with a high Q-factor and pronounced resonant properties, such as Manzanillo and Acapulco), the ''strengths'' of the recorded 2017 tsunami waves were mostly determined by distance from the source. Contrary to the maximum wave heights, the general spectral properties of the tsunami signals for all three events were highly similar at a given coastal site and mainly resemble the spectral structure of background oscillations at the same site. This similarity indicates that the frequency properties of the tsunami waveforms for a steadystate tsunami signal are mainly determined by local topographic features rather than by the source parameters. Estimates of the ''colour'' of an event (i.e., the open-ocean tsunami frequency content) show that the 2017 Chiapas tsunami was mostly ''reddish'' (long-period), with 68% (DART 43413) to 87% (DART 43412) of the total tsunami energy related to waves with periods [ 35 min. In contrast, the 2010 and 2011 tsunamis were ''reddish-blue'', with 48-57% associated with long-period waves ([ 35 min) and 52-43% with short-period waves (2-35 min). The dominant periods of the tsunami waves were mostly linked to the shape, length, and width of the source region: the larger the source and the shallower its depth, the longer the periods of the generated tsunami waves. The complicated structure of the source explains the saturated and wide frequency-band character of the tsunami spectra. Our analysis also reveals an anisotropic nature to the 2017 tsunami waves; waves that propagated northeastward along the mainland coast of North America and southeastward along the Central American coast were significantly different from those that propagated southwestward, normal to the source orientation. This aspect of the wave field appears to be related to two distinct types of waves; ''trapped (edge) waves'' retained on the shelf (which plays the role of a ''wave guide''...

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“…Most of the spectra we examined have distinct peaks that correspond to the horizontal bands of high energy evident in f‐t plots (Figures 6–8). These peaks (whose periods in minutes are indicated in Figures 11 and 12) are in good agreement with those at the same stations described for other tsunami events on this coast (Zaytsev et al., 2016, 2017, 2021). Moreover, the peaks are the same for atmospheric and oceanic tsunamis and for the background spectra.…”

“…Constructed using a multiple‐filter method (Thomson & Emery, 2014), the diagrams show the variations in the recorded tsunami waves as functions of frequency and time (cf. Rabinovich et al., 2006, 2017; Zaytsev et al., 2017, 2021). In the present case, the f‐t diagrams help separate the two types of tsunami waves (“atmospheric” and “oceanic”), enabling us to examine their transformations in the coastal zone.…”

“…The largest tsunami wave height in the southern region—164 cm—was recorded at Santa Cruz, Ecuador, located on the coast of one of the Galapagos Islands (see Figure 1). Actually, most of the listed stations recorded tsunami waves that were higher, on average, that those during other tsunami events, including the 2004 Sumatra tsunami (Rabinovich et al., 2006), the 2010, 2014 and 2015 Chilean tsunamis (Zaytsev et al., 2016), the 2011 Tohoku (Zaytsev et al., 2017) and 2017 Chiapas tsunamis (Zaytsev et al., 2021). It appears that these amplifications are related to the resonant topographic properties of the recording sites, indicating that these sites can be considered as “hot spots” for arriving tsunami waves (cf.…”

“…It seems self evident, that dissimilar generation mechanisms will also produce significantly different frequency contents for these two types of tsunami waves. To examine the spectral properties of the waves, we used the same approach used to examine the 2010, 2014, and 2015 Chilean, 2011 Tohoku and 2017 Chiapas tsunamis (Zaytsev et al., 2016, 2017, 2021).…”

“…The present study is mostly based on tide gauge and atmospheric pressure data from the coast of Mexico and adjacent regions of the Americas. Recently, we examined the tsunami impact on these regions from far‐field events in 2010, 2011, 2014 and 2015 (Zaytsev et al., 2016, 2017) and from the near‐field event in 2017 (Zaytsev et al., 2021). As a result, the individual resonant properties of the coastal stations are well known and the “ hot‐spots ” identified.…”