The Quaternary Active Faults Database of Iberia (QAFI) is an initiative lead by the Institute of Geology and Mines of Spain (IGME) for building a public repository of scientific data regarding faults having documented activity during the last 2.59 Ma (Quaternary). QAFI also addresses a need to transfer geologic knowledge to practitioners of seismic hazard and risk in Iberia by identifying and characterizing seismogenic fault-sources. QAFI is populated by the information freely provided by more than 40 Earth science researchers, storing to date a total of 262 records. In this article we describe the development and evolution of the

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The Northwest and Central-West Iberian Peninsula configure an intraplate area far from the active plate boundaries, where the Variscan basement crops out extensively (Iberian Massif). This area of the Iberian Peninsula has been traditionally considered a seismically stable region; however, it presents a moderate intraplate seismicity which indicates the presence of active structures and the occurrence of potentially damaging earthquakes. The scarcity of Mesozoic and Cenozoic deposits makes very difficult to track the record of the more recent tectonic activity and the characterization of active tectonic structures within the Iberian Massif. Nevertheless the seismic sequences of 1995-1997 in Lugo (5.1 mb; IV) and 2003 in Zamora (4.2 Mw) provided important information about the orientation of the present stress tensor, and the distribution of the hypocenters informed about the rupture geometry of the fault planes. The present work integrates geological, geomorphological, structural, and seismological data in order to define the main potentially active faults in the region. Faults trending NE-SW to N-S are potentially active as strike-slip, in some cases with a reverse component, under a NW-SE to N-S compression.

The El Salvador Fault Zone, firstly identified after the 13th February 2001 Mw 6.6 El Salvador earthquake, is a 150 km long, 20 km wide right-lateral strike-slip fault system. Ruptures along the ESFZ are thought to be responsible for most of the historical destructive earthquakes along the El Salvador Volcanic Arc, as well as for most of the current seismicity of the area. In this work, we focus on the geological setting of the fault zone by describing its geomorphology and structure, using field-based observations, digital terrain modelling, and aerial photograph interpretation with the aim at contributing to the understanding of the ESFZ slip behaviour. In particular, we address the ESFZ structure, kinematics and evolution with time.The ESFZ is a complex set of traces divided in major rupture segments characterized by different geometry, kinematics and geomorphic expressions. Natural fault exposures and paleoseismic trenches excavated along the fault show that the strike-slip deformation is distributed in several planes. Both geometry and kinematics of the fault zone are consistent with a transtensional strain regime.The estimated geological slip rate for the main fault segments by paleoseismic trenches and displaced geomorphic features implies a deficit in velocity of the fault compared to the available GPS velocities data. The high vertical scarps of some fault segments would require Quaternary slip rates not coherent neither with measured GPS velocities nor with slip rates obtained from paleoseismic analysis. This mismatch suggests a pre-existing graben structure that would be inherited from the previous regional roll back related extensional stage. We consider that the ESFZ is using this relict structure to grow up along it. As a result, we propose a model for ESFZ development consistent with all these observations. Keywords: El Salvador Fault Zone, active strike-slip fault, 13 February 2001 earthquake, geomorphology, Volcanic arc Resumen La Zona de Falla de El Salvador (ZFES) es un sistema de falla de desgarre dextral de 150 km de longitud y 20 de anchura, que fue identificada por primera vez después del terremoto de Mw 6.6 de El Salvador de febrero de 2001. La mayoría de la sismicidad y de los terremotos históricos destructivos producidos en el arco volcánico salvadoreño han sido producidos por la ruptura de la ZFES. Este trabajo se centra en el marco geológico de la zona de falla describiendo su geomorfología y su estructura a través de observaciones de campo, del estudio de los modelos digitales del terreno y de la interpretación de las fotografías aéreas, con el objetivo de avanzar en el conocimiento del comportamiento de la ZFES. En concreto trataremos del estudio de la estructura, la cinemática y la evolución de la ZFES.La ZFES es un complejo sistema de fallas divididas en varios segmentos que se diferencian en la geometría, la cinemática y la expresión geomorfológica. En los afloramientos de la falla, así como en las trincheras paleosismicas excavadas se ha observado que la deformación de d...

The earthquake was centered at 12.80° N, 88.79° W with a focal depth of 40 km, in the subduction zone between the Cocos and Caribbean plates. This earthquake was followed by numerous aftershocks with the same origin; ~540 events with M > 2 occurred in the fi rst month, and 4000 in the fi rst six months, nearly half of which were larger than M 3.0. Just one month later, on 13 February, a second major earthquake of M W 6.6 occurred, this time located farther inland Geological Society of America Special Paper 375 2004

It has long been recognized that earthquakes change the stress in the upper crust around the fault rupture and can influence the behaviour of neighbouring faults and volcanoes. Rapid estimates of these stress changes can provide the authorities managing the post-disaster situation with valuable data to identify and monitor potential threads and to update the estimates of seismic and volcanic hazard in a region. Here we propose a methodology to evaluate the potential influence of an earthquake on nearby faults and volcanoes and create easy-to-understand maps for decision-making support after large earthquakes. We apply this methodology to the Mw 7.8, 2016 Ecuador earthquake. Using Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) and continuous GPS data, we measure the coseismic ground deformation and estimate the distribution of slip over the fault rupture. We also build an alternative source model using the Global Centroid Moment Tensor (CMT) solution. Then we use these models to evaluate changes of static stress on the surrounding faults and volcanoes and produce maps of potentially activated faults and volcanoes. We found, in general, good agreement between our maps and the seismic and volcanic events that occurred after the Pedernales earthquake. We discuss the potential and limitations of the methodology.

SUMMARY Seismic data recorded from a temporary network deployed at the western edge of the Pyrenees is used to study the aftershocks series following a magnitude 4.1 earthquake that took place on 2002 February 21, to the NW of Pamplona city. Aftershock determinations showed events distributed between 1 and 4 km depth in a small active area of about 4 km2, E–W oriented delineating the southern sector of the Aralar thrust unit. This seismogenic feature is supported by focal solutions showing a consistent E–W nodal plane with normal faulting following the main strike‐slip rupture. The Aralar structure with its shallow activity may be interpreted as a conjugate system of the NE–SW deep‐seated Pamplona active fault nearby. Cross‐correlation techniques and relative location of event clusters further constrained the epicentral domain to 2 km long and 1 km wide. Statistical relations and parameters established indicate a rather low b‐value of 0.8 for the Gutenberg–Richter distribution, denoting a region of concentrated seismicity, and a P‐parameter of 0.9 for the Omori's law corresponding to a low decay of the aftershock activity in this area. More than 100 aftershocks were accurately located in this high‐resolution experiment, whereas only 13 of them could be catalogued by the permanent agencies in the same period, due to a much sparser distribution. The results enhance the importance of using dense temporary networks to infer relevant seismotectonic and hazard constraints.

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