Lorca Earthquake Research Articles

Geological evidences of surface rupture related to a seventeenth century destructive earthquake in Betic Cordillera (SE Spain): constraining the seismic hazard of the Alhama de Murcia fault

Constraining the date of the last major event occurred in a fault is of paramount importance in probabilistic seismic hazard assessment when time-dependent models are considered. Eight of the twelve destructive earthquakes occurred in the eastern Betic Cordillera since sixteenth century, are located less than 10 km away from the Alhama de Murcia fault (AMF). Up to now, it has not been identified any geological evidence on the ground surface to associate these events with the activity of specific fault sections of the AMF. In this work we present the first geological evidence of the catastrophic 1674 event occurred at Lorca (SE Spain). The excavations carried out at La Torrecilla Creek exposed archaeological remains from the Islamic period (VIII–XIII centuries in this region) affected by 55 ± 20 cm offset by the AMF fault. This event reached intensity VIII and produced 30 fatalities at Lorca for an estimated population of 7300 inhabitants. This supports the occurrence of earthquakes with surface rupture in the historical epoch on the Alhama de Murcia fault and reinforces the results obtained in previous paleoseismological work. The theoretical scenarios of maximum magnitudes and recurrence time obtained by combining this historical event with the fault slip rate allow us to conclude that the seismic hazard associated with maximum magnitude events in this section could be high. In addition, the static Coulomb stress transferred to the Gonar–Lorca section by the 2011 (Mw 5.2) Lorca earthquake may have significantly increased the hazard.

Significance of directivity effects during the 2011 Lorca earthquake in Spain

The May 11th 2011, Lorca earthquake in Southeastern Spain was a moderate magnitude event (Mw 5.1) yet it caused nine fatalities, more than 300 injuries and more than 462 million euros in economic loses. Peak ground accelerations as well as response spectral ordinates far exceed expected values from various ground motion prediction models. In particular, spectral ordinates computed from recorded ground motions significantly exceed those in current Spanish probabilistic seismic hazard models, as well as those in the Spanish and European building codes. The objective of this paper is to assess directivity effects on ground motions recorded during the 2011 Lorca earthquake, and to evaluate the significance of these effects in earthquake resistant design on moderate seismic regions. In the first part of this paper, we study the likelihood of the presence of a directivity pulse, by conducting a comparison of different parameters of recorded ground motions to analytical pulses. In the second part, we relate the recorded ground motion and its inelastic displacement spectra to some recent statistical models that try to capture the displacement demand features of earthquakes presenting directivity-pulse characteristics. It is shown that simple analytical pulses are capable of reproducing very well pulse-type near-fault ground motions recorded during the event. It is concluded that directivity effects played a major role in the large impact caused by this relatively small event. Furthermore, directivity effects which are typically ignored, both in probabilistic seismic hazard analysis and in most building codes, may lead to important underestimations of ground motions.

La comunicación de crisis en la administración pública española: análisis de evidencia empírica

Catástrofes, terremotos, pandemias, enfermedades epidémicas, emergencias y la alteración de los servicios básicos son sólo algunos de los acontecimientos impredecibles que muestran de qué manera las crisis pueden desarrollarse con gran rapidez y la importancia que tiene para los gobiernos y las administraciones públicas gestionar efectivamente su comunicación de crisis.La experiencia de crisis nacionales (la política detrás de la crisis del Ébola, el terremoto de Lorca, el movimiento vecinal de Gamonal en Burgos, la huelga no autorizada de los controladores aéreos en 2010 o el accidente de tren en Angrois) muestran que la comunicación efectiva requiere una extensa preparación y este artículo presenta un trabajo empírico sobre la comunicación de crisis de las administraciones públicas en España.El objetivo de esta investigación es describir el estado de la práctica de la comunicación de crisis en la administración del Estado, comunidades autónomas y municipios, con el apoyo en las percepciones de sus trabajadores. Para lograrlo, realizamos un estudio a través de encuesta con referencias a casos de crisis gestionados por la Administración Pública española.

The 2011 Mw 5.2 Lorca earthquake as a case study to investigate the ground motion variability related to the source model

Near-field recordings are very sensitive to the spatiotemporal details of the rupture process while far-field signals show the signature of the overall “point-source” earthquake mechanism. Near- and far-field recording ranges are dependent on the event magnitude and modulate the variability of the ground motion. This study investigates the ground motion and the source-related near-field variability for the 2011 Lorca earthquake, a moderate seismic event (Mw = 5.2) that caused significant localized damage in the Region of Murcia, Spain. The low-frequency content (up to 1 Hz) is simulated by the wavenumber integration method assuming four different source models obtained by inversion of geodetic or seismological data. As a first result, we estimate the variability of the ground motion. We observe that the dispersion in the peak and spectral parameters is larger at LOR, the closest station to the source, and decreases as the source distance increases (more than 50 km far from the source) where the finite-fault effects become negligible. The variability of the pseudo spectral velocity at 2 s is within the ground motion prediction equation ±1 σ, apart from the very near-source station and those stations affected by forward directivity effects. These effects are also found in high-frequency seismograms obtained by the empirical Green’s functions approach.

ESI-07 ShakeMaps for instrumental and historical events in the Betic Cordillera (SE Spain): An approach based on geological data and applied to seismic hazard

This work presents high-resolution ShakeMaps for three earthquakes occurred in the Betic Cordillera (SE Spain): the 2011 CE Lorca event (VIII ESI-07), the 1863 CE Huércal-Overa event (VIII ESI-07) and the 1829 CE Torrevieja event (X ESI-07). Detailed field characterizations and mapping of their coseismic environmental effects (EEEs) are catalogued and classified following the ESI-07 scale. The resulting macroseismic information reaches up to ten times the existing information based on conventional damage-based scales (e.g. EMS-98), providing a better constrain towards more realistic ground-motion scenarios. The 2011 Lorca earthquake has been used as a calibration event, since there is a relevant record of instrumental measures on source, and ground-motion parameters allowing a direct comparison with the modelled PGA values. From a methodological standpoint, the obtained ShakeMaps follow the basic guidelines and methodology proposed by the USGS ShakeMap Program. The two historical earthquakes analysed in this paper produced a wide variety of secondary EEEs but no surface faulting was reported. These effects need to be properly identified by high-resolution DTMs (5 m/pixel), far from the c. 900 m/pixel terrain models used by USGS program. Additionally, the proposed ESI-07 ShakeMaps incorporate correction factors to solve inconsistencies derived from the large scale terrain models considered in standard USGS program workflows: (1) empirical slope-derived Vs30 models result in overestimations of the PGA values in flat terrains in absence of unconsolidated deposits; (2) the topographic amplification factor included here, explains the occurrence of rock-falls and landslides in steep areas, where ground motion is underestimated by the sole use of slope-derived Vs30 models. Basic geological and geomorphological information need to be implemented in the modelling workflow in both cases. To prevent PGA overestimations in flat terrains a correction factor related to the spatial distribution and thickness of the Quaternary unconsolidated deposits has been incorporated (i.e. isopach maps). To correct PGA underestimations in steep terrains an amplification factor was modelled following standard guidelines of seismic topographic amplification.The comparison via iteration of the spatial distribution of both ESI effects and EMS macroseismic data, with the obtained ground-motion spatial distribution, enables a better definition of the geological parameters for the studied historical earthquakes. A more accurate location and/or size of the suspect seismic sources are obtained for these historical earthquakes, providing scenarios more realistic than those resulting from old intensity maps. Quaternary Geology and Geomorphology are behind the implementation of the proposed ESI-07 ShakeMaps, being especially useful when exploring historic or ancient moderate earthquakes with scarce damage-based macroseismic data, but with sufficient paleoseismic or archaeoseismic records. In summary, the methodological workflow proposed here contemplates the implementation of a computational configuration seismologically relevant and able to test repeated seismic scenarios, with different parametric data, in a controlled GIS environment useful to reproduce historical events.

Next Future Large Earthquake in Romania: A Disaster Waiting to Happen?

Romania has one of the highest seismic‐hazard levels in Europe. The recent study by Pavel et al. (2016) shows that around two‐thirds of the country (over 150,000 km2) has an expected peak ground acceleration in excess of 0.2 g (value with 10% probability of exceedance in 50 years). In this article, the possible impact and the institutional response in the event of a future large earthquake are discussed in the light of a several recent events and studies. Romania is mainly affected by earthquakes occurring in the Vrancea intermediate‐depth seismic source. Nevertheless, large magnitude crustal earthquakes can occur in several locations throughout Romania. The 1916 Fagaras earthquake, with an estimated moment magnitude ( M w) of 6.4, was the largest crustal earthquake that occurred in Romania in the twentieth century. It struck mainly an uninhabited area, and thus its impact was limited (descriptions of its effects are also very limited). However, the experience and the information gathered from other shallow earthquakes in 1981 (an earthquake with M w 5.1, and focal depth h of 15 km near the Danube Delta), in 1991 (three earthquakes in the western part of Romania with magnitudes M w 5.5), and in 2014 (a M w 5.4 and h =41 km earthquake in the Vrancea region) have shown that this type of earthquake can cause significant structural damage, panic, and even casualties. The recent experience of the Lorca earthquake in Spain (2011) with regard to structural damage and losses due to a relatively small magnitude shallow‐focus earthquake ( M w 5.1) occurring close to a densely populated area is also worth considering (Hermans et al. , 2014). Other likely candidates for a potentially destructive local crustal earthquake include (Bala et al. , 2015) the Transylvania seismic source that has not generated any significant earthquake ( M w>5.0) since 1880 and is …

Resolution of rupture directivity in weak events: 1‐D versus 2‐D source parameterizations for the 2011, Mw 4.6 and 5.2 Lorca earthquakes, Spain

AbstractResolving robust source parameters of small‐moderate magnitude earthquakes is still a challenge in seismology. We infer directivity from apparent source time functions (ASTFs) at regional distance and quantify the associated uncertainties. ASTFs are used for (i) modeling a propagating 1‐D line source from the duration data and (ii) inverting the 2‐D slip distribution from the full signals. Slip inversion is performed through a Popperian scheme, where random trial models are either falsified on account of large misfit, or else become members of the solution set of the inverse problem. We assess the resolution of rupture directivity representing centroid shifts from the solution set in a rose diagram. Using as example an event with well‐studied rupture directivity, the 2011 Mw 5.2 Lorca (Spain) earthquake, 1‐D and 2‐D parameterizations yield similar estimates for direction (N213°E and N220°E, respectively) and asymmetry (67:33, 65:35) of rupture propagation, as well as rupture length (2.1 km, 2.7 km) and speed (3.5 km/s, 3.25 km/s). The high rupture velocity ≥ 90% vS may be held primarily responsible for the strong directivity effect of this earthquake. We show that inversion of apparent source durations is intrinsically unable to resolve highly asymmetric bilateral ruptures, while inversion of full ASTFs misses part of the signal's complexity, suggesting the presence of deconvolution artifacts. We extend the analysis to the Mw 4.6 foreshock of the Lorca earthquake, inferring similar directivity parameters and slip pattern as for the mainshock. The rupture toward SW of both earthquakes suggests that this direction could be inherent to the fault segment.

Planificación de la vivienda de emergencia en desastres naturales: Terremotos de Haití y España

The goal of this research is to critically review the role played by the Spanish Red Cross in the provision of temporary housing in the aftermath of the Haiti and Lorca earthquakes and develop recommendations about pre-disaster planning which Spain and other developed countries must have. Despite the economic and development gap between Haiti and Spain and the enormous disproportion between both earthquakes in 2010 and 2011, respectively, the Spanish Red Cross provided the same temporary housing according to the minimum housing standards set out by the 2004 Sphere Project. This paper shows that the indiscriminate application of the minimum standards set out be the Esfera project may lead to the rejection of this kind of dwellings in industrialized countries and as a result lead to delay, improvisation and increase in the price of solutions eventually adopted. Therefore, the recommendation for these countries is to develop a set of regulations and a proper planning for the provision of temporary housing with requirements proportionate to their standards of living.

Learning from RC building structures damaged by the earthquake in Lorca, Spain, in 2011

Abstract In May 2011, the city of Lorca, in Spain, suffered an earthquake of magnitude M w = 5.1. Even though the intensity was not particularly high, as the epicentre was only a few kilometres away from the city severe damage was caused to many buildings. The movements generated by the earthquake, together with the special characteristics of the reinforced concrete (RC) building structures in the region, gave rise to different types of structural damage, which are analysed and classified in this paper. After carrying out inspections on buildings in the town itself, a number of deficiencies responsible for the damage caused were detected in RC elements, as well as behavioural alterations caused by non-load-bearing walls. Variations in the local or general stiffness due to staircases, which are usually considered to be secondary elements, were another factor that played a role in the buildings' response. From the study we learned a number of lessons about what happened in Lorca and these should be borne in mind in the future when designing RC building structures in areas prone to earthquakes.

Reassessment of intensity estimates from vulnerability and damage distributions: the 2011 Lorca earthquake

This paper presents a reassessment of the seismic intensity estimated for the 2011 Lorca (southeastern Spain) earthquake based on detailed vulnerability data and its comparison with the observed damage. Building and urban data are gathered in selected areas during a field campaign and are completed with office work. The significance of vulnerability modifiers in the final vulnerability distribution is analyzed, and their relation with observed damage trends is explored. A direct application of the vulnerability modifiers is not capable of reproducing the observed damage patterns. A significant increase of vulnerability related to the performance of buildings presenting soft story is required to reach a damage distribution consistent with intensity estimates in the study areas. Accordingly, an intensity increase in certain study zones (as compared to other areas of the city of Lorca) is suggested. Although the approach followed in this study is applied in a city of Spain, it can be extrapolated to other areas where detailed vulnerability assessment is feasible and damage data are available.

PATRONES CULTURALES DEL PERIODISMO DE FUENTES: LA GESTIÓN DE LA COMUNICACIÓN SOBRE EMERGENCIAS EN LA ADMINISTRACIÓN PÚBLICA EN ESPAÑA. LA CRISIS DEL ÉBOLA Y EL TERREMOTO DE LORCA

The activity of informing is not only based on getting the information; there is a branch or culture called “Source journalism” that provides data to journalists, who report directly to citizens. It is known as “source journalism” because it is done from the information source. The professionals affliated to this branch or journalistic culture are usually the so-called Communication Directors (Dircom). For the administration, the function of informing is an obligation based on the 20th article of the Constitution. From that article derives the right of the citizens to get information about the activities of the administration, those activities can be general or particular according to the interests or fundamental rights of a person. As a consequence, the administration is an information source for journalists. This work is about the peculiarities of performing the public function of informing as part of the administration and about the vicissitudes to which Communication Directors are subjected. The practical cases analyzed are the management of the Public Information during the Lorca earthquake in 2011 and the media crisis in Spain derived from the Ebola virus in 2014.

Would RC wide-beam buildings in Spain have survived Lorca earthquake (11-05-2011)?

Lorca earthquake (11-05-2011) is most destructive event recorded in Spain, causing nine fatalities and other severe consequences. Its important intensity was rather unexpected, and serious concern arose regarding risk of building stock in Spain. This paper analyzes performance, under Lorca earthquake, of RC buildings with one-way slabs with wide beams. This construction type is chosen for its high vulnerability and for being vastly widespread in Spain. This study is conducted on 3 and 6-story prototype representative buildings. These buildings are designed for three major seismic zones in Spain: low seismicity, moderate seismicity (as Lorca) and medium seismicity (as Granada). Seismic performance under Lorca earthquake is numerically investigated through nonlinear time-history analyses. Results show that buildings designed without any seismic provision (i.e. those in low seismicity zones) do not survive Lorca record, even with cooperation of masonry infill walls. Buildings with seismic design (i.e. those in Lorca and Granada zones) can survive Lorca earthquake only with collaboration of infill walls. To raise reliability of these conclusions, a sensitivity analysis to most influencing parameters is conducted.

Recorded Ground Motion and Estimated Soil Amplification for the 11 May 2011 Lorca Earthquake

On 11 May 2011 an earthquake of magnitude 5.2 ( M w) hit the Murcia region of Spain causing significant damage to buildings in the town of Lorca. Accelerograms were recorded by stations of the Instituto Geográfico Nacional, and high-amplitude ground motions were observed at the Lorca station, with a peak ground acceleration (PGA) of 0.37 g. The contribution of a near-field component of ground motion is shown in time histories and in elastic response spectra. Features of near-field ground motions such as directivity could have significantly enhanced the ground shaking caused by this event. Local amplification effects in Lorca were investigated by the H/V spectral ratio technique and an array method. Information obtained from the geophysical field survey allowed the definition of representative soil columns and site classifications according to Eurocode 8. Modeling of site response is conducted for an example location. The aftershocks recorded at different sites confirm the soil amplification at these locations.

Comportamiento de los edificios de HA con tabiquería durante el sismo de Lorca de 2011: aplicación del método FAST

A back analysis aimed at the evaluation of reinforced concrete frame buildings performance during the 2011 Lorca, Spain, earthquake is provided by applying FAST method. This is a simplified approach for the estimation of largescale vulnerability of RC moment resisting frame buildings. It accounts for the structural contribution of non-structural masonry infills. Lorca earthquake showed a Peak Ground Acceleration (PGA) three times higher with respect to that recommended by local design code. However, damage observed seldom included building collapses. Characteristics of the seismic event and features of the local building stock are studied aimed at showing, through the application of FAST, whether the low amount of collapses could be a consequence of the additional contribution provided by infills, despite their non-structural role in local code design framework. FAST damage scenario showed a fair agreement with observed damage, providing a confirmation on the structural role played by masonry infills.

Archaeoseismological Analysis of a Late Bronze Age Site on the Alhama de Murcia Fault, SE Spain

An archaeoseismological study of Tira del Lienzo (Totana, Spain) was undertaken. The site belongs to the Argar archaeological group (2200–1550 cal. B.C.; Bronze Age). It is located on the trace of the reverse left‐lateral Alhama de Murcia fault (AMF) that was responsible for the 5.1 Mw 2011 Lorca earthquake. The constructive typology of the site consists of mortar‐free irregular natural boulders (dry‐set masonry) and differs from earlier archaeoseismological sites built on regular masonry constructions in the Betic Cordillera. Four Earthquake Archaeological Effects (EAEs) were identified as follows: (1) an apparent surface rupture (c. 18 cm left‐lateral offset), (2) the differential coseismic uplift of several centimeters affecting the main building of the settlement, (3) the widespread development of fractures on the ground surface (ground cracks) in a NE‐SW direction consistent with the kinematics of the AMF, and (4) fractures in boulders that constitute the remains of the dry stone walls at the site. Structural analysis of the two fracture types reveals two nearly orthogonal sets (NE‐SW and NW‐SE), matching the strike‐slip kinematics of the AMF in the zone. Archaeoseismic evidence and related radiocarbon dates of the different building phases of the Bronze Age site indicate the probable occurrence of at least one strong seismic event (6.3–6.5 Mw; IX ESI‐07) around 1550 cal. B.C., or soon after, triggering the destruction and probably the eventual abandonment of the site. We have identified an ancient lost earthquake from the Bronze Age and report the first archaeoseismological evidence of surface rupture in the Iberian Peninsula. This study also provides the first numerical data in the Totana‐Alhama segment of the AMF based on the recorded archaeoseismic displacements. These data allowed us to characterize the related slip rates (0.05 mm/yr) to define the seismic potential of the analyzed fault segment of the AMF, which was poorly defined by previous seismic and geological data.

CAPjoint, A Computer Software Package for Joint Inversion of Moderate Earthquake Source Parameters with Local and Teleseismic Waveforms

Accurate earthquake source parameters such as fault mechanism, depth, and moment magnitude are not only important in seismic‐hazard assessment, but also are crucial to studies of earthquake rupture processes and seismotectonics. Although large earthquakes (M_w 7+) may cause substantial damage, they occur less frequently. In contrast, moderate earthquakes (M_w 5.0–6.5) occur with much higher frequency and may occur on faults not geologically identified. Some of the moderate earthquakes cause damage in densely populated communities, especially in developing countries (Baumbach et al., 1994; Hamzehloo, 2005). For example, the 2011 M_w 5 earthquake in Lorca, Spain (Pro et al., 2014), the 2012 M_w 5.9 Ferrara earthquake sequence in northern Italy (Malagnini et al., 2012), the 2010 M_w 5 Suining earthquake in Sichuang Province of China (Luo et al., 2011), and the 1998 M_w 5.7 Zhangbei earthquake in Hebei Province of China (Li et al., 2008) all caused substantial economic loss and casualty. Compared with events larger than M_w 7, rupture processes of these moderate events can be approximated as point sources, which are usually described with a centroid moment tensor (CMT) because the rupture duration is usually shorter than the period used in the waveform inversion.

The new sismimur plan: seismic urban planning in the region of murcia (spain) after the earthquake of may 11, 2011

The Lorca earthquake of May 11, 2011, was a traumatic yet very instructive experience for the Region of Murcia. Despite its limited scale of only 5.1 Mw, the earthquake caused nine deaths and material damage valued at over 800 million Euros in a city of just 100,000 inhabitants. This catastrophic result has led the regional government to implement a new plan, SISMIMUR, to better foresee and manage future earthquakes. In a move to improve the response to earthquakes, the new plan will incorporate innovative approaches to seismic engineering, creating aftershock evaluation protocols for buildings and the implementation of urban planning to reduce seismic vulnerability in the territorial development of cities. In these fi elds, the government of the Region of Murcia has commissioned the Technical University of Cartagena to conduct an urban microzonation in the city of Lorca as a pilot project to incorporate its fi ndings to the future plan SISMIMUR. This article summarizes the main advances achieved in this research project and their possible contributions to the SISMIMUR plan.

Resilience in workers and residents of a Centre for the Elderly institutionalized

Resilience is a dynamic and multidimensional construct that refers to the ability of people to cope with or recover successfully from adverse situations. The aim of this study was to analyze resilience in workers and residents of a Centre for the Elderly institutionalized according to sociodemographic characteristics (sex, age and marital status) after the adverse situation caused by an earthquake in Lorca in May 2011. A sociodemographic questionnaire developed ad hoc and the adaptation of the Resilience Scale Connor-Davidson (CD-RISC) were administered. Participants were 20 workers and 34 seniors in a Centre for the Elderly institutionalized in the Region of Murcia (Lorca). The average age of the institutionalized seniors was 81 years with a standard deviation of 7.68 and the average age of professional caregivers was 37.85 years with a standard deviation of 9.60. The study allows to determine resilience capacity in response to sociodemographic characteristics and the existence of significant mean differences between the ability of tenacity-efficacy among workers and residents of the Centre for the Elderly. This will allow to design actions to prevent and/or intervene promptly.

Resilience in workers and residents of a Centre for the Elderly institutionalized

Resilience is a dynamic and multidimensional construct that refers to the ability of people to cope with or recover successfully from adverse situations. The aim of this study was to analyze resilience in workers and residents of a Centre for the Elderly institutionalized according to sociodemographic characteristics (sex, age and marital status) after the adverse situation caused by an earthquake in Lorca in May 2011. A sociodemographic questionnaire developed ad hoc and the adaptation of the Resilience Scale Connor-Davidson (CD-RISC) were administered. Participants were 20 workers and 34 seniors in a Centre for the Elderly institutionalized in the Region of Murcia (Lorca). The average age of the institutionalized seniors was 81 years with a standard deviation of 7.68 and the average age of professional caregivers was 37.85 years with a standard deviation of 9.60. The study allows to determine resilience capacity in response to sociodemographic characteristics and the existence of significant mean differences between the ability of tenacity-efficacy among workers and residents of the Centre for the Elderly. This will allow to design actions to prevent and/or intervene promptly.

Earthquake rupture propagation inferred from the spatial distribution of fault rock frictional properties

The frictional properties of fault rocks that rupture during earthquakes are expected to affect the nucleation and propagation of seismic slip, but these properties and their variation under in-situ earthquake conditions are typically unknown. Here, we present experimental results on the variation of frictional properties of fault rocks from the Alhama de Murcia Fault (AMF) in SE Spain, which ruptured in the 2011 Lorca earthquake. In the epicentral area, the fault zone is characterized by the presence of abundant phyllosilicate-rich gouges that surround more competent, fractured lenses of the phyllitic basement. Measurements of lineaments and orientations of R-shears in the gouges are consistent with CMT-solutions of the 2011 Lorca earthquake, suggesting that the bulk of displacement on the AMF was accommodated within similar gouges at depth. In order to evaluate the frictional properties of the fault rocks of the AMF, we performed rotary shear experiments under hydrothermal conditions of samples obtained from surface outcrops of the AMF zone, progressively simulating deeper levels in the crust by stepping temperature, effective normal stress and fluid pressure. A negative velocity-dependence of friction, expressed as a negative value of the Rate-and-State Friction (RSF) parameter (a−b) and which is a prerequisite for the nucleation of an instability, was observed only for samples derived from competent lenses under hydrothermal conditions. Gouge-derived samples exhibited only velocity-strengthening properties, i.e. positive values of (a−b), which increase with deeper conditions, in particular with increasing effective normal stress. Combined with our outcrop observation of the anastomosing nature of gouges surrounding more competent lenses of fractured protolith, our results suggest that the 2011 Lorca earthquake nucleated in the competent lenses, followed by propagation of slip into the frictionally weaker gouges. The inferred upward propagation direction of the 2011 Lorca earthquake is consistent with propagation of the rupture into the velocity-strengthening gouges which at shallower levels provide a smaller barrier to seismic slip due to lower values of effective normal stress and (a−b). Our results suggest that the spatial variation of the frictional properties along the AMF was an important factor controlling the nucleation and propagation of seismic slip which, together with the shallow hypocenter close to the city of Lorca, led to serious damage. We infer that understanding of such variations in frictional properties may significantly improve seismic hazard evaluations in tectonically active regions.