Tsunami

Tectonics and seismic potential along the Caribbean subduction zone in northwestern Colombia based on GeoRED GPS data

A dissertation for the degree of Doctor in Science Department of Earth and Environmental Sciences Graduate School of Environmental Studies, Nagoya University

ABSTRACT

The Caribbean coast of northwestern Colombia is a region where complex tectonic interactions are taking place between the main oceanic Caribbean plate and several continental blocks known as North Andean, Panamá, Maracaibo, and Bonaire blocks. The existence or lack of subduction of the Caribbean plate beneath the North Andean block margin has been a matter of debate given the absence of a well-defined Wadati-Benioff zone and shallow seismic (and tsunami) activity in instrumental and historical written records. As a result, studies to decipher the Caribbean’s seismic/tsunami potential are far from sufficient, which translates into potentially ignored hazards that could have large impacts on the region. Then, it is essential to carry out analyses on this subject.

Existence of an earthquake cycle and seismic potential along a plate subduction zone can be identified through geodetic approaches. Recent dense precise GNSS observations around the world revealed significant strain accumulation during the interseismic period. I made use of the improved spatio-temporal dataset from the GeoRED project (GEOdesia: Red de Estudios de Deformación in Spanish) of the Geological Survey of Colombia (SGC) to determine interseismic velocities of 87 continuous GPS sites for the period 2008-2017 under the ITRF2014 reference frame. Based on these data, I described motion trends of interacting tectonic plates/blocks in Colombia, which shows general consistency with previous studies. Thanks to the improved spatial resolution of the network, a new tectonic affiliation in the northern part of the country named Macondo block is identified. This interpretation contradicts the previous tectonic framework and has important implications regarding the plate kinematics in northwestern Colombia with a very slow subduction of the Caribbean plate at about 7 mm/yr. In addition, a prevailing compressive pattern of deformation is revealed from horizontal displacement rates, which concentrate mostly along subduction and collision margins, including the Caribbean subduction zone with strain rates of ~65 nanostrain/yr.

The localized contraction at the Caribbean coast of Colombia is intriguing. In order to elucidate if it is due to an ignored seismic potential, an interplate coupling analysis is conducted by inverting 3-dimensional GPS data assuming an elastic half-space medium. The results revealed a locked region on the plate interface offshore Cartagena city, which could cause a Mw8.0 earthquake every ~600 yr based on the size of the locked region and the slow subduction velocity of the Caribbean plate with respect to the Macondo Block. This seismic event could potentially trigger a tsunami

considering the shallowness of the asperity. This interpretation seems to be validated by the consideration of the Caribbean northwestern Colombia as one of the slowest subduction zones characterized by “invisible” megathrust earthquakes and tsunamis occurring over very long recurrence intervals and for which, there is a lack of historical records as well as geological studies. Although the model explains horizontal deformation, a remaining problem is the reproduction of vertical motions, in particular, the large coastal subsidence.
Assuming the Caribbean coast of Colombia is the locus of a future megathrust event that is approaching the final stage of the interseismic period, new modeling is conducted to improve overall data fitting, especially in the vertical component, by taking a regular recurrence of large earthquakes and viscoelastic relaxation of the asthenosphere into account, since it has been proved significant when the recurrence interval is much longer than the relaxation time. Also, the sensitivity of surface deformation to parameters such as the lithospheric thickness, the asthenospheric viscosity, and the earthquake recurrence interval is tested. This modeling attempt confirms the Caribbean subduction zone as a potential locus of a Mw8.1 type earthquake with a recurrence interval still consistent with the absence of historical records and previous estimates. It also reproduces observed velocities to a better degree than the elastic coupling model according to 3-dimensional WRMS values. In this regard, it is demonstrated that early postseismic effects following an earthquake play an important role in increasing interseismic coastal subsidence and then, have important implications regarding the correct interpretation of the geodetic data in terms of seismic and tsunami hazards. Coseismic and postseismic uplift at coastal regions are completely recovered in one earthquake cycle, suggesting that tectonic activity at the subduction interface does not leave a permanent signature in the coastal topography. Regarding the tested parameters, the lithospheric thickness acts as a controlling parameter of the deformation, but the viscosity or recurrence interval assumptions are insensitive and cannot be constrained from the available observation data.

Both the elastic and viscoelastic models conclude the Caribbean subduction zone can potentially generate a Mw8.0 – Mw8.1 earthquake possibly followed by a tsunami in northwestern Colombia for which there is no adequate hazard mitigation and management plans. Besides, if the event takes place in the near future, regional impacts would be devastating. Despite the fact there are no historical records, the absence of these events should not be taken lightly. The slow nature of the

subduction zone produces megathrust over long recurrence times (several hundreds or thousands of years), which cause the earthquakes remain disguised in a seismic quiescence. It remains a challenge for forthcoming studies to integrate paleoseismology and paleotsunami information to corroborate the present dissertation hypothesis and to improve the seismic potential assessment in the Caribbean of Colombia. Additionally, reconciliation of short- and long-term strain inconsistency can be provided by acquiring new geodetic and geological data (older marine terraces) in order to reduce the uncertainties of each observation. Subsequent modeling is needed to solve the time scale discrepancy and to propose a full contemporary/long-term interpretation of the deformation signals.

Date
2023
Data type
Research report
Theme
Research and monitoring
Document
Report number
Graduate School of Environmental Studies, Nagoya University 2023
Geographic location
Bonaire

Tsunamis in the Caribbean Sea – Implications from coarse-clast deposits and the importance of their shape

This presentation gives an overview of the results of a five-year research project on tsunami-induced boulder transport. It stresses the importance of the exact determination of boulder shapes in contrast to simplified bodies (such as cuboids), especially with regard to the transport distance. It also provides insights about a newly developed numerical boulder-transport model based on Pudasaini (2012). Additionally, some ideas how experimental research on tsunami-induced boulder transport may be improved and coordinated in the future will be presented.

The investigations by physical experiments are based on three boulder shapes of which one depicts the replica of an original boulder from the island of Bonaire (Caribbean Sea, Lesser Antilles). The experiments clearly reveal that the available impact area of the boulder has a great significance; however, this is so far insufficiently considered in analytical equations. In the given case, the comparison between the more streamline-shaped replica of the Bonaire boulder and an idealised cuboid boulder resulted in reduced transport distances of 30 %, in average. Additionally, statistical evaluations revealed that the entire process is highly sensitive with partly stochastic behaviour. Thus, we support the statement of Bressan et al. (2018) in this regard. We show, how important it is to calculate and communicate wave thresholds for mobilisation in terms of probability ranges instead of fixed values.

Based on the results of our own physical experiments and the evaluation of published physical experiments, we developed a tool, which supports researchers in assessing the accuracy of analytical equations for specific in-situ settings (Oetjen et al., 2021). This tool encompasses the crucial parameters (e.g., bottom roughness, boulder shape), combines their influence on the transport process and finally gives an indication of whether the present conditions tend to amplify or hamper the boulder transport. The benefit and the usage of the above-mentioned tool will be demonstrated exemplarily.

Furthermore, within the framework of the project a numerical Boulder-Transport-Model was developed which is based on the Immersed Boundary Method and the Two-Phase Flow Model of Pudasaini (2012). Insights into the functionality of the model and the importance of the increased flow density will be highlighted, while the further development steps will be indicated.

As part of the project, we also dealt with the future development of research on tsunami-induced boulder transport (cf. Oetjen et al., 2021). One important suggestion is to establish a standardised reference setup for experimental investigations within the research community. It would enable researchers to compare the results of their own experiments and the effect of the investigated parameters with well-documented reference values and assist them to evaluate and classify their experimental results accordingly.

Date
2022
Data type
Other resources
Theme
Research and monitoring
Geographic location
Bonaire

Tsunami hazard assessment on Bonaire based on sedimentary traces of prehistoric high-energy waves

The Caribbean region is highly vulnerable to coastal hazards since a relatively high percentage of the population lives right at the coast. Tourism, a major economic factor on many islands, is concentrated in coastal areas as well. The “traditional” hazards along the coasts of the Caribbean, as perceived some decades ago, are earthquakes, volcanism and storm surges during hurricanes. This focus is justified in the light of the devastating earthquake of Haiti in 2010, which represents a regional maximum in magnitude with a death toll of more than 230,000. The eruption of Mount Pelée on Martinique, which destroyed St. Pierre, the former principal town of the island, and killed around 28,000 inhabitants, and the Great Hurri-cane of 1780 with a similar number of fatalities along the Antilles island arc were outstanding disasters in terms of magnitude. Moreover, the frequency during the 500 years of historical documentation is high as well.
However, history tells that the Caribbean is also prone to the risk of tsunamis. One hundred twenty-seven possible tsunamis were documented during the last 500 years, of which 53 were finally considered to be real tsunamis.

Tsunami hazard on Bonaire
Since we found geological traces of potential tsunamis at almost all sites investigated along the coast of Bonaire, we consider the entire coastline to be prone to tsunami hazard. Along the windward coast, the largest boulders point to the occurrence of tsunami wave heights in the order of 8-10 m. This height estimate is similar to tsunami wave heights observed at the Venezuelan coast in historical times, e.g. at Paria in 1530 or at Puerto Tuy in 1900 [5]. The minimum inundation of such a tsunami on the carbonate platform along the windward side would be 300 m, possibly even more than 500 m. However, findings of candidate tsunami deposits in the sediment cores of the bays, bokas and saliñas, such as Boka Bartol, Saliña Tam or Lagun far inland indicate that especially these low-lying areas provide pathways for inundation and destruction by a tsunami. Thus, a low topography, as found on the entire southern part of Bonaire, is more prone to tsunami inundation.

Date
2012
Data type
Other resources
Theme
Research and monitoring
Geographic location
Bonaire

Potential and limits of combining studies of coarse- and fine-grained sediments for the coastal event history of a Caribbean carbonate environment

The coastal deposits of Bonaire, Leeward Antilles, are among the most studied archives for extreme-wave events (EWEs) in the Caribbean. Here we present more than 400 electron spin resonance (ESR) and radiocarbon data on coarse-clast deposits from Bonaire’s eastern and western coasts. The chronological data are compared to the occurrence and age of fine-grained extremewave deposits detected in lagoons and floodplains. Both approaches are aimed at the identification of EWEs, the differentiation between extraordinary storms and tsunamis, improving reconstructions of the coastal evolution, and establishing a geochronological framework for the events. Although the combination of different methods and archives contributes to a better understanding of the interplay of coastal and archive-related processes, insufficient separation, superimposition or burying of coarse-clast deposits and restricted dating accuracy limit the use of both fine grained and coarse-clast geoarchives to unravel decadal- to centennial-scale events. At several locations, distinct landforms are attributed to different coastal flooding events interpreted to be of tsunamigenic origin. Coastal landforms on the western coast have significantly been influenced by (sub)-recent hurricanes, indicating that formation of the coarse-clast deposits on the eastern coast is likely to be related to past events of higher energy.

 

Date
2013
Data type
Scientific article
Theme
Research and monitoring
Geographic location
Bonaire

Coastal stratigraphies of eastern Bonaire (Netherlands Antilles): New insights into the palaeo-tsunami history of the southern Caribbean

Abstract:

A sediment record of three alluvial sites along the east- and northeast-oriented shore of Bonaire (Netherlands Antilles) provides evidence for the recurrence of several extraordinary wave impacts during the Holocene. The interpretation of onshore high-energy wave deposits is controversially discussed in recent sedimentary research. However, it represents a powerful tool to evaluate the hazard of tsunami and severe storms where historical documentation is short and/or fragmentary. A facies model was established based on sedimentary and geochemical characteristics as well as the assemblage and state of preservation of shells and shell fragments. Radiocarbon data and the comparison of the facies model with both recent local hurricane deposits and global “tsunami signature types” point to the occurrence of three major wave events around 3300, 2000–1700 and shortly before 500 BP. Since (i) the stratigraphically correlated sand layers fulfill several sedimentary characteristics commonly associated with tsunamis and (ii) modern strong hurricanes left only little or even no sediment in the study areas, they were interpreted as tsunamigenic. However, surges largely exceeding the energy of those accompanying modern hurricanes in the southern Caribbean cannot entirely be ruled out. The results are partially consistent with existing chronologies for Holocene extreme wave events deduced from supralittoral coarse-clast deposits on Aruba, Bonaire and Curaçao as well as overwash sediments from Cayo Sal, Venezuela. 

Date
2010
Data type
Scientific article
Theme
Research and monitoring
Geographic location
Bonaire