SZ4D International Webinar this Friday, September 25th | 9:00 am PDT

SZ4D Office contact at
Thu Sep 24 18:47:43 UTC 2020

*Unearthing geological and historical evidence of large
earthquakes and tsunamis on the Mexican Subduction Zone – results,
problems and future studies*
*Professor María-Teresa Ramírez-Herrera*

Pre-register for the webinar at:

Globally, instrumentally based assessments of tsunamigenic potential of
subduction zones have underestimated the magnitude and frequency of great
events because of their short time record. Historical and sediment records
of large earthquakes and tsunamis have expanded the temporal data and estimated
size of these events. Instrumental records suggest that the Mexican
Subduction earthquakes produce relatively small tsunamis, however
historical records and now geologic evidence suggest that great earthquakes
and tsunamis have whipped the Pacific coast of Mexico in the past. The
sediment marks of centuries-old-tsunamis validate historical records
and indicate
that large tsunamigenic earthquakes have shaken the Guerrero-Oaxaca region
in southern Mexico and had an impact on a bigger stretch of the coast than
previously suspected. We present the first geologic evidence of great
tsunamis near the trench of a subduction zone previously underestimated as
a potential source for great earthquakes and tsunamis. Two sandy tsunami
deposits extend over 1.5 km inland of the coast. The youngest tsunami
deposit is associated with the 1787 great earthquake, M 8.6, producing a
giant tsunami that poured over the coast flooding 500 km alongshore the
Mexican Pacific coast and up to 6 km inland. The oldest event from a less
historically documented event
occurred in 1537. The 1787 earthquake, and tsunami and a probable
predecessor in 1537, suggest a plausible recurrence interval of 250 years.
We have also reported on geologic evidence of other historical and
earthquakes and their tsunamis, and of coastal coseismic deformation on the
Oaxaca, Guerrero and Jalisco coast of the Mexican subduction zone.
Furthermore, our observations based on a combination of geologic and historic
evidence, together with modelling results, imply that this subduction zone
is also subject to long-fault ruptures near the trench capable of producing
large tsunamis. Indeed subduction zones might have variable rupture modes,
long- and short-fault ruptures, along the Middle American trench. We show
that the common belief that great earthquakes and tsunamis do not occur on
the Mexican Pacific coast cannot be sustained.

Paleoseismology and tsunami deposits studies have provided new insights
into the understanding of the Mexican and other subduction zones, and still
remain several unresolved questions and challenges. We will summarize
questions, challenges, and strategies that could help solve some of them.

*SZ4D presents International Webinars, a series where the working groups
invite international scientists to present on different topics relevant to
their research and region. SZ4D values international voices and invites you
to learn from these folks.*
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