East African Rifting; Seismic Contribution
Eloumala Onana Parfait Noel,
FEUMOE Alain Narcisse,
NJITEU TCHOUKEU Cyrille Donald,
EBODE Brice Valentin,
NGATCHOU Evariste,
EMVOUTOU C Huguette,
MOUZONG Pemi Marcelin
This study interprets the rifting mechanism and lithospheric state within the East African Rift-System,
revealing a system in moderate state, active extension distension driven by distributed strain and
magma-assisted rifting. Analysis of a six-month seismic catalog shows that seismicity is predominantly
low-to-moderate in magnitude (Mb: 3.7 to 4.5), with a maximum of Ms up to 5.3. The absence of large-
magnitude events (M > 7) indicates that regional extension is accommodated incrementally through a
steady sequence of moderate earthquakes and secondary processes, such as magmatic intrusion and
creep, rather than the catastrophic release of massive stored stress.
A pronounced Mb-versus-Ms discrepancy where Ms is significantly higher, points to shallow focal
depths and longer rupture durations. This shallow nature of seismicity is further reflected in the catalog
with 0.0 km fixed depth data artifacts, confirming that considerable tectonic energy originates within
the uppermost crust (1–2 km). Crucially, a near-total absence of seismicity below 12 km identifies a
remarkably shallow brittle-ductile transition zone. This compressed brittle layer indicates an elevated
geothermal gradient and active lithospheric thinning, where an upwelling asthenosphere heats the
lower crust, forcing it to deform plastically. Consequently, the tectonic forces are entirely localized
within a thin, highly fractured upper crust from 0 to 15 km. Unable to store the considerable elastic
strain required for large events, this brittle upper crust fails frequently and easily along a network of
normal faults, effectively bleeding off tectonic energy through continuous moderate swarms.
