TY - JOUR A1 - Melnick, Daniel A1 - Moreno, Marcos A1 - Motagh, Mahdi A1 - Cisternas, Marco A1 - Wesson, Robert L. T1 - Splay fault slip during the M-w 8.8 2010 Maule Chile earthquake JF - Geology N2 - Splay faults are thrusts that emerge from the plate boundaries of subduction zones. Such structures have been mapped at several convergent margins and their activity commonly ascribed to large megathrust earthquakes. However, the behavior of splay faults during the earthquake cycle is poorly constrained because typically these structures are located offshore and are difficult to access. Here we use geologic mapping combined with space and land geodesy, as well as offshore sonar data, to document surface-fault ruptures and coastal uplift at Isla Santa Maria in south-central Chile (37 degrees S) caused by the 27 February 2010 Maule earthquake (M-w 8.8). During the earthquake, the island was tilted parallel to the margin, and normal faults ruptured the surface and adjacent ocean bottom. We associate tilt and crestal normal faulting with growth of an anticline above a blind reverse fault rooted in the Nazca-South America plate boundary, which slipped during the Maule earthquake. The splay fault system has formed in an area of reduced coseismic plate-boundary slip, suggesting that anelastic deformation in the upper plate may have restrained the 2010 megathrust rupture. Surface fault breaks were accompanied by prominent discharge of fluids. Our field observations support the notion that splay faulting may frequently complement and influence the rupture of subduction-zone earthquakes. Y1 - 2012 U6 - https://doi.org/10.1130/G32712.1 SN - 0091-7613 VL - 40 IS - 3 SP - 251 EP - 254 PB - American Institute of Physics CY - Boulder ER - TY - JOUR A1 - Melnick, Daniel A1 - Cisternas, Marco A1 - Moreno, Marcos A1 - Norambuena, Ricardo T1 - Estimating coseismic coastal uplift with an intertidal mussel calibration for the 2010 Maule Chile earthquake (M-w=8.8) JF - Quaternary science reviews : the international multidisciplinary research and review journal N2 - Coseismic coastal uplift has been quantified using sessile intertidal organisms after several great earthquakes following FitzRoy's pioneer measurements in 1835. A dense survey of such markers may complement space geodetic data to obtain an accurate distribution of fault slip and earthquake segmentation. However, uplift estimates based on diverse intertidal organisms tend to differ, because of few methodological and comparative studies. Here, we calibrate and estimate coastal uplift in the southern segment of the 2010 Maule, Chile earthquake (M-w = 8.8) using > 1100 post-earthquake elevation measurements of the sessile mussel Perumytilus purpuratus. This mussel is the predominant competitor for rocky shores all along the Pacific coast of South America, where it forms fringes or belts distinctively in the middle intertidal zone. These belts are centered at mean sea level and their width should equal one third of the tidal range. We measured belt widths close to this value at 40% of the sites, but overall widths are highly variable due to the unevenness in belt tops; belt bases, in turn, are rather regular. Belt top unevenness apparently results from locally-enhanced wave splash, whereas belt base evenness is controlled by predation. According to our measurements made beyond the earthquake rupture, the belt base is at the bottom of the middle intertidal zone, and thus we propose to estimate coastal uplift using the belt base mean elevation plus one sixth of the tidal range to reach mean sea level. Within errors our estimates agree with GPS displacements but differ from other methods. Comparisons of joint inversions for megathrust slip suggest combining space geodetic data with estimates from intertidal organisms may locally increase the detail of slip distributions. KW - Coastal uplift KW - Maule earthquake KW - Chile KW - Intertidal organisms KW - Perumytilus mussels KW - Slip distribution Y1 - 2012 U6 - https://doi.org/10.1016/j.quascirev.2012.03.012 SN - 0277-3791 VL - 42 IS - 5 SP - 29 EP - 42 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Melnick, Daniel A1 - Moreno, Marcos A1 - Cisternas, Marco A1 - Tassara, Andres T1 - Darwin seismic gap closed by the 2010 Maule earthquake JF - Andean geology N2 - The Maule earthquake (Mw 8.8) that affected south-central Chile on February 27, 2010 was preceded by the 1835 event documented by FitzRoy and Darwin. The relation between both events has been controversial. Fault slip in 2010 estimated by Lorito et al. (2011) is less than expected from 175 years of strain accumulation, leading them to conclude only limited overlap between the 2010 and 1835 events, and that a Mw 7.5-8 event could still strike the Concepcion region. However, Lorito et al.'s model was based on displacements obtained from only 6 GPS stations and underpredicts observations from recent studies. Here we show that an alternative model based on 169 GPS displacements reproduces the data better, suggesting Lorito et al.'s main conclusion is not correct. Based on a slip deficit map, we suggest the seismic gap opened in 1835 was most likely closed in 2010. KW - Maule earthquake KW - Coseismic slip distribution KW - Slip deficit KW - Seismic gap Y1 - 2012 U6 - https://doi.org/10.5027/andgeoV39n3-a11 SN - 0718-7092 VL - 39 IS - 3 SP - 558 EP - 563 PB - Servicio Nacional de Geologìa y Minerìa CY - Santiago ER - TY - JOUR A1 - Lange, Dietrich A1 - Tilmann, Frederik A1 - Barrientos, Sergio E. A1 - Contreras-Reyes, Eduardo A1 - Methe, Pascal A1 - Moreno, Marcos A1 - Heit, Ben A1 - Agurto, Hans A1 - Bernard, Pascal A1 - Vilotte, Jean-Pierre A1 - Beck, Susan T1 - Aftershock seismicity of the 27 February 2010 Mw 8.8 Maule earthquake rupture zone JF - Earth & planetary science letters N2 - On 27 February 2010 the M-w 8.8 Maule earthquake in Central Chile ruptured a seismic gap where significant strain had accumulated since 1835. Shortly after the mainshock a dense network of temporary seismic stations was installed along the whole rupture zone in order to capture the aftershock activity. Here, we present the aftershock distribution and first motion polarity focal mechanisms based on automatic detection algorithms and picking engines. By processing the seismic data between 15 March and 30 September 2010 from stations from IRIS, IPGP, GFZ and University of Liverpool we determined 20,205 hypocentres with magnitudes M-w between 1 and 5.5. Seismic activity occurs in six groups: 1.) Normal faulting outer rise events 2.) A shallow group of plate interface seismicity apparent at 25-35 km depth and 50-120 km distance to the trench with some variations between profiles. Along strike, the aftershocks occur largely within the zone of coseismic slip but extend similar to 50 km further north, and with predominantly shallowly dipping thrust mechanisms. Along dip, the events are either within the zone of coseismic slip, or downdip from it, depending on the coseismic slip model used. 3.) A third band of seismicity is observed further downdip at 40-50 km depth and further inland at 150-160 km trench perpendicular distance, with mostly shallow dipping (similar to 28 degrees) thrust focal mechanisms indicating rupture of the plate interface significantly downdip of the coseismic rupture, and presumably above the intersection of the continental Moho with the plate interface. 4.) A deep group of intermediate depth events between 80 and 120 km depth is present north of 36 degrees S. Within the Maule segment, a large portion of events during the inter-seismic phase originated from this depth range. 5.) The magmatic arc exhibits a small amount of crustal seismicity but does not appear to show significantly enhanced activity after the M-w 8.8 Maule 2010 earthquake. 6.) Pronounced crustal aftershock activity with mainly normal faulting mechanisms is found in the region of Pichilemu (similar to 34.5 degrees S). These crustal events occur in a similar to 30 km wide region with sharp inclined boundaries and oriented oblique to the trench. The best-located events describe a plane dipping to the southwest, consistent with one of the focal planes of the large normal-faulting aftershock (M-w = 6.9) on 11 March 2010. KW - Maule 2010 earthquake KW - local seismicity KW - aftershock distribution KW - subduction zone KW - Central Chile KW - seismogenic zone Y1 - 2012 U6 - https://doi.org/10.1016/j.epsl.2011.11.034 SN - 0012-821X VL - 317 IS - 2 SP - 413 EP - 425 PB - Elsevier CY - Amsterdam ER -