Thermal regime from bottom simulating reflectors along the north Ecuador–south Colombia margin: Relation to margin segmentation and great subduction earthquakes

Abstract

[1] The north Ecuador-south Colombia (NESC) margin has three transverse morphotectonic segments (the Manglares, Tumaco, and Patia segments), each with different tectonic and structural patterns. Following the 1906 subduction earthquake, the NESC margin has been the site of three megathrust events in 1942, 1958, and 1979 for which the rupture zones abut one another. We first investigated variations in heat flow derived from bottom simulating reflectors (BSR) observed along multichannel seismic lines sampling the three morphotectonic segments. Strong along-strike variations of the BSR-derived heat flow, just landward of the deformation front, suggest that each morphotectonic segment has a specific thermal regime. Finite element thermal models show that these variations are mainly produced by changes in the age and the dip of the oceanic plate and local hydrothermal cooling. We then examined the relationship between seismogenesis and thermal structure along the plate boundary. The updip limits of the 1942 and 1979 seismogenic zones, estimated from the aftershock area and rupture zone, reach the trench, where the temperature at the top of the subducting plate appears to be 50°-60°C. Between these events the seismogenic zone of the 1958 earthquake is restricted to a region landward of a prominent outer basement high where the temperature appears to be 100°-120°C. We propose that on the NESC margin the updip limit of the seismogenic zone is primarily controlled by low-temperature processes except for the 1958 event for which the seismogenic updip limit appears to be related to a structural feature in the upper plate.

Origin of a crustal splay fault and its relation to the seismogenic zone and underplating at the erosional north Ecuador–south Colombia oceanic margin

“…In northern Ecuador, the temperature and depth burials of splay fault SF1 and deep segment of the SC appear lower than the temperature and greater than the depth burials of the splay fault in the Shimanto accretionary complex. According to thermal modeling [ Marcaillou et al , 2006], splay fault SF1 cuts the thermal structure between ∼50°C and 140°C at depths of 6–15 km, and the failure of the 1958 earthquake initiated at 160–170°C, and ∼19‐km depth, where the plate interface tends to parallel the thermal structure (Figure 3b). Such differing depths and temperatures along splay faults in Japan and Ecuador may be explained by the diverse methods used to determine fossil and present‐day temperatures, but also by their different fault dip geometry, lower plate age, and contrasting basement rheologies and mineralogies, i.e., sedimentary in Japan and oceanic in Ecuador.…”

“…Older horses could have been destroyed by subduction erosion. Note that isotherms [ Marcaillou et al , 2006] crosscut the splay faults and tend to parallel the interplate fault.…”

“…The 1958 focal mechanism [ Swenson and Beck , 1996] is projected on the interplate fault. Seaward extent of 1958 brittle coseismic slip matches with splay fault SF1.White dash lines are isotherms in °C projected from thermal model calculated for adjacent line SIS‐42 [ Marcaillou et al , 2006]. (c) Blocky velocity model from Agudelo [2005] showing velocity layers and isovelocity contours in km/s.…”

Thermal environment of the Southern Washington region of the Cascadia subduction zone

“…Q B is the bathymetrically corrected heat flow, resulting in Q BSR , the basal heat flow with effects of sediment accumulation removed. Based on the uncertainties associated with the BSR heat flow calculation (supporting information), the calculated uncertainty of the BSR heat flow is approximately ±10%, similar to previous estimates [ Davis et al ., ; Marcaillou et al ., ], with a maximum of ±18% for areas of rapid bathymetric variations.…”

How wide is the seismogenic zone of the Lesser Antilles forearc?

“…These dehydration reactions (illite to smectite and opal to quartz) begin at temperatures of 60-100 o C and continue to about 150 o C [Moore and Saffer, 2001]. Thus, 150 o C is considered by most workers to be the beginning of true stick-slip "seismogenic" behavior, with transitional behavior to about 100 o C or perhaps lower Oleskevich et al, 1999;Gutscher and Peacock, 2003;Marcaillou et al, 2006]. The simple conceptual model that interplate earthquake rupture can only occur along the contact zone between the oceanic crust of the downgoing plate and the crystalline crust of the upper plate [Byrne et al, 1988] has been disproved by the rupture zones of recent mega-thrust earthquakes in Sumatra 2004[Lay et al, 2005, Chile 2010 [Vigny et al, 2011] and Japan [Simmons et al, 2011;Lay et al, 2011] where in all three cases, rupture and thrust mechanism aftershocks extended to within 20 km of the trench.…”