A thesis submitted to the Faculty of Science, University of the Witwatersrand, in fulfilment of the requirements for the degree of Doctor of Philosophy University of the Witwatersrand School of Geosciences and Dublin Institute for Advanced Studies School of Cosmic Physics Geophysics Section February 2016 / Archean cratons, and the Proterozoic orogenic belts on their flanks, form an integral part of the Southern Africa tectonic landscape. Of these, virtually nothing is known of the position and thickness of the southern boundary of the composite Congo craton and the Neoproterozoic Pan African orogenic belt due to thick sedimentary cover. In this work I present the first lithospheric-scale geophysical study of that cryptic boundary and define its geometry at depth. The results are derived from two-dimensional (2D) and three-dimensional (3D) inversion of magnetotelluric data acquired along four semi-parallel profiles crossing the Kalahari craton across the Damara-Ghanzi-Chobe belts (DGC) and extending into the Congo craton. Two dimensional and three-dimensional electrical resistivity models show significant lateral variation in the crust and upper mantle across strike from the younger DGC orogen to the older adjacent cratons. The Damara belt lithosphere is found to be more conductive and significantly thinner than that of the adjacent Congo craton. The Congo craton is characterized by very thick (to depths of 250 km) and resistive (i.e. cold) lithosphere. Resistive upper crustal features are interpreted as caused by igneous intrusions emplaced during Pan-African magmatism. Graphite-bearing calcite marbles and sulfides are widespread in the Damara belt and account for the high crustal conductivity in the Central Zone. The resistivity models provide new constraints on the southern extent of the greater Congo craton, and suggest that the current boundary drawn on geological maps needs revision and that the craton should be extended further south. The storage possibilities for the Karoo Basins were found to be poor because of the very low porosity and permeability of the sandstones, the presence of extensive dolerite sills and dykes. The obvious limitation of the above study is the large spacings between the MT stations (> 10km). This is particularly more limiting in resolving the horizontal layers in the Karoo basin. However the 1D models provide layered Earth models that are consistent with the known geology. The resistivity values from the 1D models allowed porosity of the Ecca and Beaufort group lithologies to be calculated. It is inferred that the porosities values are in the range 5-15 % in the region below the profile. This value is considered too low for CO2 storage as the average porosity of rock used for CO2 is generally more than 10 to 12 percent of the total rock unit volume.

A dissertation submitted to the Faculty of Science, University of Witwatersrand in the fulfilment of the requirements for the degree of Master of Science. Johannesburg, 2015. / Northwest Botswana holds a key position for the correlation of the Pan-African mobile belts of southern Africa (i.e. the Damara-Zambezi-Lufilian Orogeny). Phanerozoic cover (Kalahari Group) precludes direct correlation between Proterozoic lithologies of the Damara Belt and thick metasedimentary sequences of northwest Botswana. A combination of new geological and geophysical field observations, interpretation of 50 m resolution aeromagnetic data, and 2.2 km resolution gravity data of Namibia and Botswana, have led to the development of a new sub- Kalahari geological map of the Damara Belt and northwest Botswana. The interpretation of potential field and magnetotelluric (MT) data complemented with both new and published geological data, has improved the identification of the northern and southern margins of the Damara Belt and northwest Botswana, and tectonostratigraphic zones within them. In addition, these correlations have established that the northern margin of the Kalahari Craton on geological maps extends further north than previously noted. The northeast trending Damara Belt is confidently traced into northwest Botswana (Ngamiland) to ~19.5°S, 22.0°E. At this location, in map view, aeromagnetically interpreted structures follow a radial distribution from northwest-striking in the west to northeast-striking in the east. The lithostratigraphic units to the north of this location cannot be confidently correlated with lithostratigraphic units of the Damara Belt. Instead, these units are better correlated with lithostratigraphic units in southern Angola and/or Zambia. The southeastern margin of the Damara Belt is in tectonic contact with the northern margin of the Ghanzi-Chobe Belt as identified in the aeromagnetic images. The Ghanzi-Chobe Belt is correlated with the Sinclair Supergroup in the Rehoboth Subprovince in Namibia. The basal Kgwebe volcanics are correlated with the Oorlogsende Porphyry Member and Langberg Formation and the unconformably overlying metasediments of the Ghanzi Group are correlated with the metasediments of the Tsumis Group. The correlations are based on similar aeromagnetic signatures, lithologies, mineralisation and age dates constrained by carbon isotope chemostratigraphy. Physical property measurements were collected on Meso- to Neoproterozoic lithologies of the Damara Belt, northwest Botswana and Zambia. The measurements included hand held magnetic susceptibility measurements on 303 samples and density measurements on 174 samples. The measurements provide one of the largest physical property databases for Namibia, Botswana and Zambia. In general, the sedimentary units have the lowest magnetic susceptibility values of ~0.207 x 10-3 SI units, respectively. The exceptions are the iron formation and diamictite of the Chuos Formation and conglomerate of the Naauwpoort Formation of 15.2 x 10-3 SI units. The iron iii formation ranges in magnetic susceptibility from 3.34 x 10-3 SI units to 92.0 x 10-3 SI units and the diamictite has a magnetic susceptibility of 7.68 x 10-3 SI units. The igneous lithologies have a density and magnetic susceptibility range from 2.58 g.cm-3 to 3.26 g.cm-3 and 0.001 x 10-3 SI units to 11.6 x 10-3 SI units, respectively. The lower values are associated with pegmatites and rhyolites and the higher values are associated with mafic lithologies and magnetite bearing granites (Omangambo, Salem, Sorris-Sorris and Red Granites). The metamorphic lithologies have the widest range of density and magnetic susceptibility values, between 2.61 g.cm-3 and 3.37 g.cm-3, and -0.299 x 10-3 SI units and 49.5 x 10-3 SI units, respectively. The lower values are associated with low grade metamorphic facies of sedimentary origin, and the higher values are associated with high-grade metamorphic facies of an igneous origin. The first upper crustal-scale interpretation of the Southern African MagnetoTelluric EXperiment (SAMTEX) was developed. The results were derived from 1D Occam inversion models, at depth intervals of 1 – 5 km, 1 – 15 km and 1 – 35 km. The MT data were acquired across the semiparallel, north-south striking DMB, NEN and OKA-CAM profiles in the vicinity of the Namibia – Botswana border between 2006 and 2009. Beneath the MT profiles are two zones of enhanced conductivity, a northern and southern zone. The enhanced conductivity of the northern zone (> 100 Ωm) is associated with individual geological bodies. The southern zone forms an elongated belt of enhanced conductivity (> 300 Ωm) at a depth of less than 5 km. This zone of enhanced conductivity is associated with Proterozoic plate boundaries and subduction zones. Three ~350 km long, north-south trending magnetic profiles were 2D forward modelled to investigate the proposed northward subduction of oceanic crust and subsequently a portion of the Kalahari Plate beneath the Congo Craton. Additionally, the folding pattern of the Ghanzi- Chobe Belt was developed. The interpretation of the magnetic models suggests a northward subduction is a possible cause for the evolution of the Damara Orogen with the regionally eastwest striking negative aeromagnetic anomaly, in northern Namibia, being caused by a thick package (~12 km to 20 km) of metasediments with a modelled magnetic susceptibility of 0. 829 x 10-3 SI units. The Damara Orogen has passed through the subduction-collisional transition but did not evolve into a large-hot orogen. Evidence suggests that the Damara Orogen has gone through the transition of subduction of oceanic crust to terrane accretion (speculated to be represented by the Deep-Level Southern Zone and Chihabadum Complex) and continental collision. However, the doubly vergent wedges did not evolve into an orogenic plateau completing the transition from a small-cold orogen to a large-hot orogen. This is similarly observed in the Alps Orogeny.

La théorie de la tectonique des plaques permet de décrire les mouvements de premier ordre qui opèrent à la surface de la Terre. S'il est acquis que la convection dans le manteau terrestre en est le moteur, les liens entre les phénomènes profonds et les caractéristiques tectoniques de la surface restent largement méconnus. Jusqu'à très récemment, les modèles de convection du manteau terrestre ne produisaient pas de tectonique de surface pouvant être comparée à celle de la Terre. Récemment, des modèles globaux de convection qui reproduisent une tectonique de surface comparable à la Terre au premier ordre ont été mis au point. Ces modèles produisent des courants mantelliques ascendants et descendants de grande échelle et des déformations localisées en surface dans les zones de divergence et les zones de convergence. Ils génèrent une expansion des fonds océaniques de manière auto-cohérente proche de celle reconstruite pour les 200 derniers millions d'années de l'histoire de la Terre et une dérive de continents similaire à celle observée grâce au paléomagnétisme. Cette thèse s'inscrit parmi les premières tentatives d'utilisation de modèles de convection sphériques auto-organisés à des fins de compréhension de la tectonique de surface. La tectonique produite dans ce type de modèles de convection sera caractérisée finement à travers l'étude des limites de plaques, de leur agencement et de leurs vitesses de déplacement. L'objectif est de pouvoir comparer qualitativement et quantitativement les résultats des calculs de convection avec les reconstructions des mouvements de la surface terrestre grâce à la tectonique des plaques et aux observations de terrain. Dans cette optique, les limites tectoniques ont été définies à la main dans un premier temps afin de comprendre la physique qui gouverne l'agencement caractéristique des plaques tectoniques terrestres. En effet, celle-ci est composée de sept grandes plaques et plusieurs petites dont la répartition statistique indique deux processus de mise en place distincts. Nous avons déterminé les processus responsables de la mise en place de l'agencement caractéristique des plaques tectoniques en surface en faisant varier la résistance de la lithosphère. Plus la lithosphère est résistante, plus la longueur totale et la courbure des zones de subduction diminue à la surface des modèles. Cela s'accompagne également d'une diminution du nombre de petites plaques. En étudiant la fragmentation au niveau des jonctions triples, nous avons montré que les petites plaques étaient associées aux géométries courbées des fosses océaniques. En revanche, les grandes plaques sont contrôlées par les grandes longueurs d'onde de la convection mantellique. Ces deux processus impliquent deux temps de réorganisation, c'est-à-dire l'apparition et la disparition d'une plaque plongeante dans le manteau terrestre (environ 100 millions d'années) pour les grandes plaques, alors que l'échelle de temps de réorganisation des petites plaques dépend des mouvements des fosses et est ainsi plus rapide d'un ordre de grandeur. Afin d'effectuer des analyses quantitatives rapides, des méthodes d'analyse automatique de la surface et de l'intérieur des modèles ont été développées. La première technique concerne la détection automatique des plaques tectoniques à la surface des modèles (ADOPT). ADOPT est un outil de détection basé sur une technique de segmentation d'images utilisée pour détecter des bassins versants. Les champs à la surface des modèles sont transformés en reliefs, soit directement, soit après un processus de filtrage. Cette détection permet d'obtenir des polygones de plaques comparable aux analyses réalisées à la main. Une autre technique de détection a été mise au point pour étudier les panaches mantelliques [etc...] / Plate tectonics theory describes first order surface motions at the surface of the Earth. Although it is agreed upon that convection in the mantle drives the plates, the relationships between deep dynamics and surface tectonics are still largely unknown. Until recently, mantle convection models could not produce surface tectonics that could be compared to that of the Earth. New global models are able to form large-scale ascending and descending mantle currents, as well as narrow regions of localized deformation at the surface where convergence and divergence occur. These models selfconsistently generate an expansion of the oceanic floor similar to that of the last 200 million years on Earth, and continental drift similar to what can be reconstructed with palaeomagnetism. This Ph.D. thesis constitutes one of the first attempts to use self-organised, spherical convection models in order to better understand surface tectonics. Here, the tectonics produced by the models is finely charaterized through the study of plate boundaries, their organisation and their velocities. The goal is to be able to compare qualitatively and quantitatively the results of convection computations with surface motions, as reconstructed using the rules of plate tectonics and field observations. Plate boundaries emerging from the models were first traced and analyzed by hand so as to understand the physics that govern the typical organization of the tectonics plates on Earth. It is characterised by seven large plates and several smaller ones, following a statistical distribution that suggests that two distinct physical processes control the plates’ layout. We have determined the processes responsible for this distribution while varying the strength of the lithosphere (the yield stress). In our models, the stronger the lithosphere, the greater the total subduction length and their curvature, and the fewer the small plates. By studying surface fragmentation with triple junctions, we showed that the formation of small plates is associated with oceanic trench curvature. Large plates, however, are controlled by the long wavelengths of the convection cells. These two processes involve two different reorganisation times, controlled either by the accretion and the subduction of the large plates (about 100 Myrs), or by trench motions for the smaller plates. In order to improve the efficiency of our analysis, we have developed automated methods to study the surface and the interior of the models. The first technique is about detecting the tectonic plates automatically at the surface of the models. It is called ADOPT. It is a tool based on image segmentation technique to detect the watersheds. The surface fields of the convection models are converted into a relief field, either directly or using a distance method. This automatic detection allows to obtain plates polygons similar to the hand analysis. Another technique of detection has been developed to study mantle plumes. These analyzes were used to determine the driving forces behind the plates layout, to quantify the timing of reorganizations and to evaluate the implication of the models rheology on the surface distribution. These new analytical tools and the constant evolution of the quality of mantle convection models allow us to improve our understanding of the link between mantle dynamics and surface tectonics, but also to target necessary improvements in the convection models used

Abstract not available

The Alpine Fault is the major structure of the Pacific-Australian plate boundary through New Zealand�s South Island. During dextral reverse fault slip, a <5 million year old, ~1 km thick mylonite zone has been exhumed in the hanging-wall, providing unique exposure of material deformed to very high strains at deep crustal levels under boundary conditions constrained by present-day plate motions. The purpose of this study was to investigate the fault zone rheology and mechanisms of strain localisation, to obtain further information about how the structural development of this shear zone relates to the kinematic and thermal boundary constraints, and to investigate the mechanisms by which the viscously deforming mylonite zone is linked to the brittle structure, that fails episodically causing large earthquakes. This study has focussed on the central section of the fault from Harihari to Fox Glacier. In this area, mylonites derived from a quartzofeldspathic Alpine Schist protolith are most common, but slivers of Western Province-derived footwall material, which can be differentiated using mineralogy and bulk rock geochemistry, were also incorporated into the fault zone. These footwall-derived mylonites are increasingly common towards the north. At amphibolite-facies conditions mylonitic deformation was localised to the mylonite and ultramylonite subzones of the schist-derived mylonites. Most deformation was accommodated by dislocation creep of quartz, which developed strong Y-maximum crystallographic preferred orientation (CPO) patterns by prism (a) dominant slip. Formation of this highly-oriented fabric would have led to significant geometric softening and enhanced strain localisation. During this high strain deformation, pre-existing Alpine Schist fabrics in polyphase rocks were reconstituted to relatively well-mixed, finer-grained aggregates. As a result of this fabric homogenisation, strong syn-mylonitic object lineations were not formed. Strain models show that weak lineations trending towards ~090� and kinematic directions indicated by asymmetric fabrics and CPO pattern symmetry could have formed during pure shear stretches up-dip of the fault of ~3.5, coupled with simple shear strains [greater than or equal to]30. The preferred estimate of simple:pure shear strain gives a kinematc vorticity number, W[k] [greater than or equal to]̲ 0.9997. Rapid exhumation due to fault slip resulted in advection of crustal isotherms. New thermobarometric and fluid inclusion analyses from fault zone materials allow the thermal gradient along an uplift path in the fault rocks to be more precisely defined than previously. Fluid inclusion data indicate temperatures of 325+̲15�C were experienced at depths of ~45 km, so that a high thermal gradient of ~75�C km⁻� is indicated in the near-surface. This gradient must fall off to [ less than approximately]l0�C km⁻� below the brittle-viscous transition since feldspar thermobarometry, Ti-inbiotite thermometry and the absence of prism(c)-slip quartz CPO fabrics indicate deformation temperatures did not exceed ~ 650�C at [greater than or equal to] 7.0-8.5�1.5 kbar, ie. 26-33 km depth. During exhumation, the strongly oriented quartzite fabrics were not favourably oriented for activation of the lower temperature basal(a) slip system, which should have dominated at depths [less than approximately]20 km. Quartz continued to deform by crystal-plastic mechanisms to shallow levels. However, pure dislocation creep of quartz was replaced by a frictional-viscous deformation mechanism of sliding on weak mica basal planes coupled with dislocation creep of quartz. Such frictional-viscous flow is particularly favoured during high-strain rate events as might be expected during rupture of the overlying brittle fault zone. Maximum flow stresses supported by this mechanism are ~65 Mpa, similar to those indicated by recrystallised grain size paleopiezometry of quartz (D>25[mu]m, indicating [Delta][sigma][max] ~55 MPa for most mylonites). It is likely that the preferentially oriented prism (a) slip system was activated during these events, so the Y-maximum CPO fabrics were preserved. Simple numerical models show that activation of this slip system is favoured over the basal (a) system, which has a lower critical resolved shear stress (CRSS) at low temperatures, for aggregates with strong Y-maximum orientations. Absence of pervasive crystal-plastic deformation of micas and feldspars during activation of this mechanism also resulted in preservation of mineral chemistries from the highest grades of mylonitic deformation (ie. amphibolite-facies). Retrograde, epidote-amphibolite to greenschist-facies mineral assemblages were pervasively developed in ultramylonites and cataclasites immediately adjacent to the fault core and in footwall-derived mylonites, perhaps during episodic transfer of this material into and subsequently out of the cooler footwall block. In the more distal protomylonites, retrograde assemblages were locally developed along shear bands that also accommodated most of the mylonitic deformation in these rocks. Ti-in-biotite thermometry suggests biotite in these shear bands equilibrated down to ~500+̲50�C, suggesting crystal-plastic deformation of this mineral continued to these temperatures. Crossed-girdle quartz CPO fabrics were formed in these protomylonites by basal (a) dominant slip, indicating a strongly oriented fabric had not previously formed at depth due to the relatively small strains, and that dislocation creep of quartz continued at depths [less than or equal to]20 km. Lineation orientations, CPO fabric symmetry and shear-band fabrics in these protomylonites are consistent with a smaller simple:pure shear strain ratio than that observed closer to the fault core (W[k] [greater than approximately] 0.98), but require a similar total pure shear component. Furthermore, they indicate an increase in the simple shear component with time, consistent with incorporation of new hanging-wall material into the fault zone. Pre-existing lineations were only slowly rotated into coincidence with the mylonitic simple shear direction in the shear bands since they lay close to the simple shear plane, and inherited orientations were not destroyed until large finite strains (<100) were achieved. As the fault rocks were exhumed through the brittle-viscous transition, they experienced localised brittle shear failures. These small-scale seismic events formed friction melts (ie. pseudotachylytes). The volume of pseudotachylyte produced is related to host rock mineralogy (more melt in host rocks containing hydrated minerals), and fabric (more melt in isotropic host rocks). Frictional melting also occurred within cataclastic hosts, indicating the cataclasites around the principal slip surface of the Alpine Fault were produced by multiple episodes of discrete shear rather than distributed cataclastic flow. Pseudotachylytes were also formed in the presence of fluids, suggesting relatively high fault gouge permeabilities were transiently attained, probably during large earthquakes. Frictional melting contributed to formation of phyllosilicate-rich fault gouges, weakening the brittle structure and promoting slip localisation. The location of faulting and pseudotachylyte formation, and the strength of the fault in the brittle regime were strongly influenced by cyclic hydrothermal cementation processes. A thermomechanical model of the central Alpine Fault zone has been defined using the results of this study. The mylonites represent a localised zone of high simple shear strain, embedded in a crustal block that underwent bulk pure shear. The boundaries of the simple shear zone moved into the surrounding material with time. This means that the exhumed sequence does not represent a simple 'time slice' illustrating progressive fault rock development during increasing simple shear strains. The deformation history of the mylonites at deep crustal P-T conditions had a profound influence on subsequent deformation mechanisms and fabric development during exhumation.

This thesis presents elastic finite difference simulations of two dimensional wavefield propagation for line-9, recorded during the 1993 part of the multi-institutional, multi-year Mendocino Triple Junction (MTJ) Seismic Experiment. Line-9 is a high-resolution, large-aperture seismic profile oriented in north-south direction, extending from the subduction regime north of the MTJ to the transform regime south of the MTJ. Snapshots of the wavefield are recorded during the simulation to create a movie which assists with the analysis of the synthetic seismograms. The simulations are computed on a 64 processor CM-5 parallel supercomputer. First a velocity model obtained by the Mendocino Working Group is examined. The model is based on information from depth-migrated single-fold reflection profiles and tomographic inversion of first arrivals. The synthetic seismic sections show acceptable first arrival traveltime fit but fail to correctly model secondary arrivals and amplitude variations of the wavefield. Based on the shortcomings of the initial model an alternative model for the north-south line is proposed. The new model introduces several distinct structures, like a subducted Gorda plate, a slabless window, and a wedge shaped low velocity zone between Franciscan material and Gorda plate. The big difference between the two models is that the initial model is too smooth to contain any discontinuities and cannot account for any reflection arrivals. In addition all structures in the lower crust of the alternative models are located about 4 km deeper than the equivalent velocities in the initial model. The seismic sections of the alternative model show much improved traveltime and amplitude fit. Also, some characteristics of the wavefield observed in the field data (e.g. traveltime oscillations, amplitude variations, and discontinuous arrivals) are also observed in the synthetic seismograms.. The position of the southern end of the Gorda plate (SEDGE) is at 80 km in the model (39.7°N). Because of the limited resolution it is not possible to resolve whether the Gorda plate just north of the SEDGE is fragmented or continuous. To add attenuation by scattering or coda waves generation to the model, the effects of a stochastic velocity description for Franciscan rocks on the wavefield are explored. The best velocity contrast between sandstones and melange units in a bimodal, seifaffine, sinuous connected model is determined as 0.5 km/s. Stochastic models of this kind successfully model background noise and coda waves and to some degree discontinuous phases, amplitude variations, and traveltime oscillations. They cannot, however, account for the full range of characteristics observed in the field data. For this, additional large scale velocity variations must be added to the model. For the final model, the (deterministic) alternative model and the statistical description of Franciscan rocks are combined. The resulting wavefield shows good amplitude and traveltime fit and the observed wavefield characteristics are similar to the characteristics of the field data. / Graduation date: 1997 / Best scan available for figures.

Two examples of Pacific rim plate boundary deformation are presented. In the first part of the thesis crustal models are derived for the northwestern part of the Vizcaino block in California using marine seismic and gravity data collected by the Mendocino Triple Junction Seismic Experiment. A northwest-southeast trending kink in the Moho is imaged and interpreted to have formed under compression by reactivation of preexisting thrust faults in the paleoaccretionary prism at the seaward margin of the Vizcaino block. The study suggests that the deformation resulted from mainly north-south compression between the Pacific-Juan de Fuca plates across the Mendocino transform fault and predates late Pliocene Pacific-North America plate convergence. In the second part, 195 earthquakes recorded during the duration of the Southern Alps Passive Seismic Experiment (SAPSE) are analysed. Precise earthquake locations and focal mechanisms provide unprecedented detail of the seismotectonics in the central South Island. The short term (6 month) SAPSE seismicity is compared with long term (8 years) seismicity recorded by the New Zealand National Seismic network and the Lake Pukaki network. The seismicity rate of the Alpine fault is low, but comparable to locked sections of the San Andreas fault, with large earthquakes expected. Changes of the depth of the seismogenic zone, generally uniform at about 10-12 km, occur only localised over distances smaller than 30 km, suggesting that thermal perturbations must be of similar scale. This implies that the thermal effects of the uplift of the Southern Alps do not change the seismogenic depth significantly and are not in accordance with most of the present thermal models. Both the Hope and Porters Pass fault zones are seismically active and deformation is accommodated near the fault zones and in the adjacent crust. North of Mt Cook, a triangular shaped region along the Alpine fault is characterised by absence of earthquakes. We interpret this as the result of the plate boundary shift from the Alpine fault to the Hope and Porters Pass fault zones. The study region shows distributed deformation in a 60-100 km wide zone on NNE-SSW trending thrust faults and strike-slip mechanisms on transfer faults. / Graduation date: 2000 / Best scan available for black and white figures.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 162-176).

Graduation date: 1992

The earth was shown in the last century to have a surface layer composed of large plates. Plate tectonics is the study of the movement and stresses in the individual plates that make up the complete surface of the world's sphere. Two types of earthquakes are observed in the surface plates, interplate and intraplate earthquakes, which are classified, based on the location of the origin of an earthquake either between two plates or within the plate respectively. Limited work has been completed on the definition of the boundary region between the plates from which interplate earthquakes originate, other than the recent work on the Mid Atlantic Ridge, defined at two degrees and the subsequent work to look at the applicability of this degree based definition. Others suggested an alternative view of a constant width for the interplate region in recent work at Texas A&M University. The objective of the paper is to determine whether the assumption of a linear width of the region along the tectonic plate boundaries to classify earthquakes as interplate and intraplate earthquakes using accepted statistical criteria provides a better fit to the data than the constant degree definition. There are three types of interplate boundaries defined by the relative movement of the two plates to each other, which further complicates this study. The study used a nonrandom analysis of regions of the different types of boundary to compare the rate and decay of the intraplate earthquakes from a notional centerline for the known boundaries. The study used GIS software and EXCEL for the statistical analysis component of the research work. The results show that a constant width definition provides a number of advantages in determining the relative definition of interplate and intraplate earthquakes when compared to the constant degree definition developed for work on the Mid Atlantic Ridge. Further research is suggested on a randomly selected set of study sites to improve the reliability and quality of the statistical work for each type of the boundary of the tectonic plates.