Active tectonics in Quito, Ecuador, assessed by geomorphological studies, GPS data, and crustal seismicity

Abstract

The Quito Fault System (QFS) extends over 60 km along the Interandean Depression in northern Ecuador. Multidisciplinary studies support an interpretation in which two major contemporaneous fault systems affect Quaternary volcanoclastic deposits. Hanging paleovalleys and disruption of drainage networks attest to ongoing crustal deformation and uplift in this region, further confirmed by 15 years of GPS measurements and seismicity. The resulting new kinematic model emphasizes the role of the N-S segmented, en echelon eastward migrating Quito Fault System (QFS). Northeast of this major tectonic feature, the strike-slip Guayllabamba Fault System (GFS) aids the eastward transfer of the regional strain toward Colombia. These two tectonic fault systems are active, and the local focal mechanisms are consistent with the direction of relative GPS velocities and the regional stress tensor. Among active features, inherited N-S direction sutures appear to play a role in confining the active deformation in the Interandean Depression. The most frontal of the Quito faults formed at the tip of a blind thrust, dipping 40°W, is most probably connected at depth to inactive suture to the west. A new GPS data set indicates active shortening rates for Quito blind thrust of up to 4 mm/yr, which decreases northward along the fold system as it connects to the strike-slip Guayllabamba Fault System. The proximity of these structures to the densely populated Quito region highlights the need for additional tectonic studies in these regions of Ecuador to generate further hazard assessments.

Control spectra for Quito

“…The east is limited by several hills which are Puengasí (P), Ilumbisí-La Bota (ILB), towards north the Inca Calderon hill (CEI), and at the north the BellavistaCatequilla (BC), where the last moderately strong earthquake of 12 August 2014 originated, which had a magnitude of 5.1 and focal depth of 5 km (Aguiar et al, 2014). The Guayl- (Alvarado et al, 2014). labamba basin, GB, can also be observed.…”

“…(meters above sea level) and the valleys are 2400 m. The hills P, ILB, CEI, and BC have heights that vary between 100 and 300 m. They are the external signs of the existence of blind reverse faults that raise from 2 to 4 mm yr −1 (Alvarado et al, 2014) and are shown in Fig. 3.…”

“…On the bottom right side of this figure, at the slopes of the hills, the Guápulo shrine is located, and towards the north is the Metropolitan Park, where a seismic refraction study was conducted to determine the velocity of shear wave V s30 on a rocky outcrop (Castillo, 2014). Table 1 shows the segments of the thrust faults that cross the city of Quito; the length of the rupture surface was estimated by Alvarado et al (2014) and the area of rupture and the expected maximum magnitude were estimated using the equations proposal in Leonard (2010). The average dip angle of the thrust faults is 550 westward (Alvarado et al, 2014).…”

“…Table 1 shows the segments of the thrust faults that cross the city of Quito; the length of the rupture surface was estimated by Alvarado et al (2014) and the area of rupture and the expected maximum magnitude were estimated using the equations proposal in Leonard (2010). The average dip angle of the thrust faults is 550 westward (Alvarado et al, 2014). Even though a fault could be considered well known, there is always uncertainty in the determination of the parameters defining the geometry of it, which is why strongmotion models should be used to somehow minimize this uncertainty.…”

Desing Spectrums for the Central North of Qui-to and Seismic Analysis of Steel Structures Using the Capacity Spectrum Method.

“…Figure 2 shows a numerical calculation model of possible fault planes that could be generated in the case of earthquakes occuring with a burst length equal to the maximum distance of each of the fault segments. The model assumes that these events are not produced simultaneously (Alvarado et al 2014;Rivas et al 2014). The fault planes are shown projected in a horizontal plane.…”