Contrasted seismogenic and rheological behaviours from shallow and deep earthquake sequences in the North Tanzanian Divergence, East Africa

Albaric, Julie; Perrot, Julie; Déverchère, Jacques; Deschamps, A.; Gall, Bernard Le; Ferdinand, R.; Petit, Carole; Tiberi, Christel; Sue, Christian; Songo, M.

doi:10.1016/j.jafrearsci.2009.09.005

Cited by 59 publications

(95 citation statements)

References 72 publications

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“…spe 500-11 1st pgs page 6 consistent with a low geothermal gradient and mafi c lower crustal rheology (e.g., Camelbeeck and Iranga, 1996;Déverchère et al, 2001;Mulibo and Nyblade, 2009;Albaric et al, 2010). Cratonic rifts with eruptive centers within basins show seismicity restricted to the upper 15 km (e.g., Ibs-von Seht et al, 2001;Ayele, 1995;Keir et al, 2006), consistent with source depths of the largest earthquakes (e.g., Yang and Chen, 2010;Craig et al, 2011).…”

Section: A'mentioning

confidence: 82%

“…Calais et al (2008) modeled the intrusion as a 2-m-wide dike intrusion beneath the ~8-km-long zone of open fi ssures and normal faults. Nearly 55 days later, an M w 5.4 earthquake and an M w 5.5 earthquake with source depths <9 km occurred beneath a nearby volcano, Oldoinyo Lengai, which then entered into an explosive eruptive stage that continued another nine months (e.g., Vaughan et al, 2008;Albaric et al, 2010). This example demonstrates both the complex interplay between magma and faulting in the accommodation of rift deformation and the stress coupling between pressurized magma chambers and fault zone unloading and loading.…”

Section: Magmatic Rifting Cyclementioning

confidence: 89%

“…The largest earthquake in the swarm was the 17 July 2007 M w 5.9 earthquake beneath the Natron basin, in the same location, within standard errors. Between 12 and 17 July, swarms of earthquakes migrated upward and 10-15 km northeastward (Albaric et al, 2010), during a period of slow fault slip detected in GPS data . Waveform modeling of the earthquake swarms indicates slip along NE-striking faults, but the slip planes remain debated (e.g., Baer et al, 2008;Calais et al, 2008;Biggs et al, 2009).…”

Section: Magmatic Rifting Cyclementioning

confidence: 96%

“…Nearly all of the seismic energy release in the admittedly short time period of the NEIC catalogue is associated with a 3-month-long sequence of faulting, intrusion, and subsequent eruption of the carbonatitic volcano, Oldoinyo Lengai, in northeastern Tanzania in 2007 (e.g., Baer et al, 2008;Calais et al, 2008;Albaric et al, 2010;Vaughan et al, 2008). One month prior to the fi rst earthquake in the swarm (15 July 2007, M w 5.4), satellite imagery detected thermal anomalies and increased eruptive activity in the Oldoinyo Lengai crater (Vaughan et al, 2008) (Fig.…”

Section: Magmatic Rifting Cyclementioning

confidence: 99%

“…The total seismic moment release for the Eastern rift in Kenya and northern Tanzania is an order of magnitude less at 2.9 × 10 18 Nm. The Eastern rift seismic moment release is dominated by a 2-month-long sequence in 2007 of faulting, intrusion, and subsequent eruption of the carbonatitic volcano Oldoinyo Lengai in northeastern Tanzania (e.g., Calais et al, 2008;Albaric et al, 2010).…”

Section: Comparison Of Magmatic and Amagmatic Rifting Cyclesmentioning

confidence: 99%

See 4 more Smart Citations

The time scales of continental rifting: Implications for global processes

Ebinger

Wijk

Keir

2013

The Web of Geological Sciences: Advances, Impacts, and Interactions

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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

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Section: A'mentioning

confidence: 82%

Section: Magmatic Rifting Cyclementioning

confidence: 89%

Section: Magmatic Rifting Cyclementioning

confidence: 96%

Section: Magmatic Rifting Cyclementioning

confidence: 99%

Section: Comparison Of Magmatic and Amagmatic Rifting Cyclesmentioning

confidence: 99%

See 3 more Smart Citations

The time scales of continental rifting: Implications for global processes

Ebinger

Wijk

Keir

2013

The Web of Geological Sciences: Advances, Impacts, and Interactions

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Deep crustal earthquakes in North Tanzania, East Africa: Interplay between tectonic and magmatic processes in an incipient rift

Albaric

Déverchère

Perrot

et al. 2014

Geochem Geophys Geosyst

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[1] In this study, we explore the origin of lower crustal seismicity and the factors controlling rift propagation using seismological data recorded within the youngest part of the East African Rift System, the North Tanzanian Divergence (NTD). Most earthquakes below Lake Manyara occur at depth ranging between 20 and 40 km and have a swarm-like distribution. Focal mechanisms of 26 events indicate a combination of strikeslip and normal faulting involving Archaean basement structures and forming a relay zone. The derived local stress regime is transtensive and the minimum principal stress is oriented N110 E. Crustal seismic tomography reveals low-velocity anomalies below the rifted basins in the NTD, interpreted as localized thermomechanical perturbations promoting fluid release and subsequent seismicity in the lower crust. SKS splitting analysis in the NTD indicates seismic anisotropy beneath 17 stations most likely due to aligned magma lenses and/or dikes beneath the rift and to the lithospheric fabrics. Our results favor a strain pattern intermediate between purely mechanical and purely magmatic. We suggest that melt products arising from a large asthenospheric thermal anomaly enhance lithospheric weakening and facilitate faulting and creeping on critically oriented inherited structures of the Precambrian lower crust. Although the crust is unlikely weakened at a point comparable to other parts of the East African Rift System, this deep-seated thermomechanical process is efficient enough to allow slow rift propagation within the eastern Tanzanian cratonic edge.

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Spectral analysis of dike‐induced earthquakes in Afar, Ethiopia

2016

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Shallow dike intrusions may be accompanied by fault slip above the dikes, a superposition which complicates seismic and geodetic data analyses. The diverse volcano‐tectonic and low‐frequency local earthquakes accompanying the 2005–2010 large‐volume dike intrusions in the Dabbahu‐Manda Hararo rift (Afar), some with fault displacements of up to 3 m at the surface, provide an opportunity to examine the relations among the earthquakes, dike intrusions, and surface ruptures. We apply the frequency index (FI) method to characterize the spectra of swarm earthquakes from six of the dikes. These earthquakes often have broad spectra with multiple peaks, making the usual peak frequency classification method unreliable. Our results show a general bimodal character with high FI earthquakes associated with deeper dikes (top > 3 km subsurface) and low FI earthquakes associated with shallow dikes, indicating that shallow dikes result in earthquakes with more low‐frequency content and larger‐amplitude surface waves. Low FI earthquakes are more common during dike emplacement, suggesting that interactions between the dike and faults may lead to lower FI. Taken together, likely source processes for low FI earthquakes are shallow hypocenters (<3 km) possibly with surface rupture, slow rupture velocities, and interactions with dike fluids. Strong site effects also heavily influence the earthquake spectral content. Additionally, our results suggest a continuum of spectral responses, implying either that impulsive volcano‐tectonic earthquakes and the unusual, emergent earthquakes have similar source processes or that simple spectral analyses, such as FI, cannot distinguish different source processes.

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Contrasted seismogenic and rheological behaviours from shallow and deep earthquake sequences in the North Tanzanian Divergence, East Africa

Cited by 59 publications

References 72 publications

The time scales of continental rifting: Implications for global processes

The time scales of continental rifting: Implications for global processes

Deep crustal earthquakes in North Tanzania, East Africa: Interplay between tectonic and magmatic processes in an incipient rift

Spectral analysis of dike‐induced earthquakes in Afar, Ethiopia

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