The time scales of continental rifting: Implications for global processes

Abstract

The rifting cycle initiates with stress buildup, release as earthquakes and/or magma intrusions/eruptions, and visco-elastic rebound, multiple episodes of which combine to produce the observed, time-averaged rift zone architecture. The aim of our synthesis of current research initiatives into continental rifting-to-rupture processes is to quantify the time and length scales of faulting and magmatism that produce the time-averaged rift structures imaged in failed rifts and passive margins worldwide. We compare and contrast seismic and geodetic strain patterns during discrete, intense rifting episodes in magmatic and amagmatic sectors of the East African rift zone that span early-to late-stage rifting. We also examine the longer term rifting cycle and its relation to changing far-fi eld extension directions with examples from the Rio Grande rift zone and other cratonic rifts. Over time periods of millions of years, periods of rotating regional stress fi elds are marked by a lull in magmatic activity and a temporary halt to tectonic rift opening. Admittedly, rifting cycle comparisons are biased by the short time scale of global seismic and geodetic measurements, which span a small fraction of the 10 2 -10 5 year rifting cycle. Within rift sectors with upper crustal magma chambers beneath the central rift valley (e.g., Main Ethiopian, Afar, and Eastern or Gregory rifts) seismic energy release accounts for a small fraction of the deformation; most of the strain is accommodated by magma intrusion and slowslip. Magma intrusion processes appear to decrease the time period between rifting episodes, effectively accelerating the rift to rupture process. Thus, the inter-seismic period in rift zones with crustal magma reservoirs is strongly dependent upon the

A multidisciplinary study of the final episode of the Manda Hararo dyke sequence, Ethiopia, and implications for trends in volcanism during the rifting cycle

“…Dykes at rift segments frequently occur in swarms over a timescale of years separated by quiescent periods of hundreds to thousands of years, giving rise to the 'rifting cycle' (Ebinger et al 2013). Globally, rifting events occur frequently, but typically at mid-ocean ridges making them difficult to observe.…”

Earthquake Clustering and Energy Release of the African–Arabian Rift System

“…1d). Along the EAR, the amount of earthquake activity is variable and primarily correlates negatively with the degree of magmatism (Ebinger et al, 2013;Déprez et al, 2014). For example, the magma-rich Ethiopian and Kenya rifts have lower amounts of seismicity than the magma-poor Tanganyika rift in the western branch (Ebinger et al, 2013).…”

“…Along the EAR, the amount of earthquake activity is variable and primarily correlates negatively with the degree of magmatism (Ebinger et al, 2013;Déprez et al, 2014). For example, the magma-rich Ethiopian and Kenya rifts have lower amounts of seismicity than the magma-poor Tanganyika rift in the western branch (Ebinger et al, 2013). The maximum depth and the maximum magnitude of earthquakes increase southward (Craig et al, 2011), a characteristic controlled by the southward increase in lithospheric thickness and strength (Pérez-Gussinyé et al, 2009;Craig et al, 2011) and overall southward decrease in geothermal gradient and decrease in magmatic and volcanic activity (Craig et al, 2011).…”

“…South of the Main Ethiopian rift (MER) and Kenya rift forming the northern sector of the eastern branch, the majority of the extension occurs on ∼60-120-km-long border fault systems that range from a single fault on the rift valley sides to a < 50-km-wide swath of faulting (e.g., Ebinger et al, 2013). Colinear border faults commonly interact to produce discrete basins that are up to ∼200-400 km in length (Chorowicz, 2005).…”

“…1). Despite this, the spatial variability of the amount of faulting and timescales of successive earthquakes and resultant implications for seismogenic hazard remain poorly understood (e.g., Ebinger et al, 2013). To address this issue, we demonstrate the application of a method newly applied in seismology to investigate the clustering of earthquakes in East Africa to delineate and quantify behavior of discrete zones with similar seismogenic properties; such a method has the potential to be applied to other continental rifts.…”