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Fault-cored fold, Arbuckle Mountains, Oklahoma.
Strain localization and distribution in areas of tectonic extension and contraction

In areas of active tectonic extension, I explore the spatial patterns of rift faulting and their relationships with the pre-rift basement fabrics (shear zones, sutures, and metamorphic foliation).

Top: Gneissic pre-rift basement fabrics in the shoaling margins of Northern Malawi Rift. Bottom left: Satellite maps & earthquake FMS of the Northern Malawi Rift. Bottom right: Aeromagnetic imaging of pre-rift basement fabrics and buried rift faults in Northern Malawi Rift. (Kolawole et al., 2018, Tectonics)

East Africa provides an excellent location for my studies because the pre-rift basement is composed of exhumed metamorphic terranes with excellent structural complexities that are observable in the field and in high-resolution aeromagnetic datasets. Also, a lot of the rift faults are well exposed at the surface and where buried, they can be delineated in filtered aeromagnetic data and 2-D seismic reflection data (where available).

Also, earthquake records provide a useful tool to investigate the spatial patterns, kinematics, and regional stress fields of active faulting along the rift basins. Recently, I began to explore crustal deformation in the Rio Grande Rift (western U.S.), bringing in the 'lessons learned' from East Africa.

In areas of tectonic contraction, I explore the structure of basement-rooted faults in order to understand the drive of the deformation into the overlying sedimentary cover. The Anadarko Foreland Basin and Southern Oklahoma Aulacogen (SOA), which evolved as contractional and inversion intracratonic settings respectively. Using 3-D seismic reflection data and basement-penetrating well logs and drill cutting geochemical analysis, I am able to analyze the intra-sedimentary structural deformation, intra-basement and through-going structures, and assess the structural and mechanical coupling between the different structural levels.

Seismic reflection images from the Anadarko Basin, showing intra-basement reflectors (mafic sills) and basement-rooted contractional faults (Kolawole et al., 2020)
Basement structure and reactivation mechanics in areas of induced seismicity 
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Folarin Kolawole examining fractures

In many parts of the world, oil & gas activities in the continental interior basins has led to increased disposal of wastewater into the deep sedimentary sequences, leading to a surge in basement-hosted seismicity associated with reactivation of pre-existing basement faults (Ellsworth, 2013; Grigoli et al., 2017). However, in regions like the U.S. Mid-Continent where widespread seismicity is attributed to regional fluid injection, little is known of the basement structure and the susceptibility to widespread earthquake triggering.

In most places, this seismogenic basement is buried beneath >2 km sedimentary cover, but is exposed at the surface in a few areas such as southern Oklahoma (bottom left photo).

Therefore, to investigate this problem, I integrate robust multiscale (outcrop & drones) field mapping of fault zones & fracture systems, structural analyses of seismic reflection data, earthquake data, and rock mechanics experiments to investigate the pre-existing structure of the basement and the basement-rooted faults in Oklahoma that makes them so susceptible to injection induced seismicity.

Earthquakes and previously mapped faults in Oklahoma
Frictional stability of Oklahoma basement
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Investigation of intraplate earthquakes onshore and proximal offshore in the Equatorial Atlantic and West African coastal regions

Over the past decades, there had been several reports of earthquakes in the Equatorial Atlantic and West African coastal countries, areas generally known to be ‘tectonically quiescent’ (e.g., Nigeria, Ghana, Benin, Liberia, Guinea, Gabon, DRC, and Angola). My collaborators and I are utilizing a combination of geological and geophysical techniques, and seismology to investigate the origin of these tremors.

Structural geophysics of coseismic surface deformation zones
Earthquake liquefaction during 2009 Karonga earthquake

Medium to large magnitude earthquake rupture of faults at upper crustal depths are often accompanied by 1.) an upward propagation of slip and surface-breaking deformation along the fault, and/or 2.) distributed surface-breaking deformation related to coseismic liquefaction of shallowly-buried unconsolidated water-saturated sediments. I utilize field observations and high-resolution near-surface geophysics to investigate the shallow subsurface structure of such surface rupture zones, providing a non-intrusive imaging of the deformation zone. This approach is also useful for identifying buried paleoseismic structures that could guide the planning of target locations for paleoseismic trenching.

Research Approach

1) Field structural geology

- Ground-based observation and measurements in outcrops

- Drone-based observation and measurements in outcrops

2) Core analysis

- Characterization and measurements of structural deformation in core samples

3) Satellite remote sensing

- Structural measurements (and interpretations) from satellite-based remotely-sensed data

4) Geophysical imaging of subsurface structures using:

- 2D & 3D seismic reflection data

- Aeromagnetic and gravity data

- Geoelectrical imaging methods (Resistivity tomography, Electromagnetics)

- Seismology (Fault mechanism solutions and stress inversion from relocated            earthquakes)

5) Laboratory geomechanics

- Uniaxial and triaxial rock deformation experiments

- Friction experiments

- Scratch test experiments

Research Study Locations

My research locations (red footprints on the map) include the Central U.S. (specifically Oklahoma, Southern Kansas, Missouri, and Illinois), Eastern north American rifted margin (New York, New Jersey, Maine, New Hampshire), Western U.S. (Rio Grande Rift and Basin & Range), East Africa region (Malawi, Tanzania, Uganda, Kenya, Botswana, Mozambique, Botswana, DRC), Offshore Brazil, New Zealand (Northern Taranaki Basin), and West Africa (Nigeria).

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