J. M. Gaspar-Escribano

Interplay between tectonics, climate, and fluvial transport during the Cenozoic evolution of the Ebro Basin (NE Iberia)

[1] Three-dimensional modeling that integrates fluvial sediment transport, crustal-scale tectonic deformation, and lithospheric flexural subsidence is carried out to simulate the landscape and drainage evolution of the Ebro sedimentary basin (NE Iberia). The Ebro Basin underwent a long period of closed intramountain drainage as a result of tectonic topography generation at the Pyrenees, the Iberian Range, and the Catalan Coastal Range. In the late Oligocene, the Catalan Coastal Range underwent extension leading to the formation of the Valencia Trough (NW Mediterranean), but the Ebro Basin remained closed for nearly 15 Myr more before the Ebro River cut through the remnants of the topographic barrier. This drainage opening caused widespread basin incision that shaped spectacular outcrops of the syntectonic and posttectonic infill. Here we investigate the processes controlling these major drainage changes. The modeling results, constrained by a large data set on the tectonic and transport evolution of the area, predict a closed phase characterized by a large lake in the central eastern Ebro Basin. Dry climatic conditions probably lowered the lake level and contributed, together with rift flank uplift, to prolong this endorheic basin stage. The age and amount of reworked sediment after the opening are consistent with an onset of basin incision between 13 and 8.5 Ma as a result of lake capture by escarpment erosion and lake level rise associated with sediment accumulation and wetter climatic conditions. Sea level changes in the Mediterranean had no major impact in the large-scale drainage evolution of the Ebro Basin. INDEX TERMS: 1625 Global Change: Geomorphology and weathering (1824, 1886); 1815 Hydrology: Erosion and sedimentation; 3210 Mathematical Geophysics: Modeling; 3344 Meteorology and Atmospheric Dynamics: Paleoclimatology; 8102 Tectonophysics: Continental contractional orogenic belts; KEYWORDS: Pyrenees, drainage evolution, lake, sediment budget, erosion, flexure

An Overview of the Damaging and Low Magnitude Mw 4.8 La Paca Earthquake on 29 January 2005: Context, Seismotectonics, and Seismic Risk Implications for Southeast Spain

This article presents an overview of the La Paca earthquake of magnitude mbLg 4.7, which occurred on 29 January 2005, with its epicenter located near the town of Avile´s in the Murcia region in southeast Spain. Despite its low magnitude, the earthquake caused important damage in two towns of the epicentral area, La Paca and Zarcilla de Ramos. These areas recorded intensities of VI–VII (European Macroseismic Scale, 1998) and sustained estimated economic losses amounting to 10 million €. Aftershocks continued for more than 2 weeks, producing considerable alarm in the population and mobilizing emergency services from the whole region. The La Paca seismic series is the third registered in the region in the past 8 years, being preceded by the Mula (1999) and southwest Bullas (2002) seismic series. These main events had also low magnitudes (mbLg 4.8) and caused damage levels similar to the 2005 earthquake. The case is an example of a moderate seismic zone where low-magnitude and frequent earthquakes have important implications on the seismic hazard and risk of the region. Although these are not the largest expected earthquakes, they have yielded important information for improving the knowledge of the seismic activity of the area. With this aim in mind, different topics have been analyzed from a multidisciplinary perspective, including seismicity, local tectonics and surface geology, focal mechanisms, macroseismic effects, and ground motion. Results indicate a local tectonic interpretation, consistent with a strike-slip focal mechanism, the confirmation of a triggering process between the 2002 and 2005 earthquakes, a geotechnical and ground-motion characterization for the damaged sites (supporting local amplification effects and estimated peak ground acceleration values of �0.1g), and an understanding of damage patterns in relation to local building trends. The results may be used as guidelines for future revisions of the Spanish Building Code (Norma de la Construccio´n Sismorresistente Espan˜ola [NCSE-02], 2002). The study results should contribute to risk mitigation in a region where strong-motion records from the maximum expected earthquakes are not available. This approach can be extended to other regions with similar seismic backgrounds and a lack of strong-motion records.

Mechanical (de-)coupling of the lithosphere in the Valencia Through (NW Mediterranean): What does it mean?

We study the mechanics of lithospheric decoupling in continental extensional basins in relation to the distribution of (non-)competent mechanical layers within the lithosphere and the position of the isostatic compensation level. We specifically address the different modes of deformation taking place in crustal levels according to a self-consistent formulation of the concept of mechanical decoupling. Subsequently, we investigate the style of lithospheric decoupling in the Valencia Trough (NW Mediterranean), a prime example of a young continental rift basin. During its evolution, the lower crust (or at least part of it) acted as a weak, non-competent layer that eventually flowed laterally to accommodate deformation in the subcrustal lithosphere and overlying crust, which became mechanically decoupled. We use a numerical model to discern whether these two layers deformed fully independently (vertical decoupling), or maintaining a mechanical link (horizontal and partial decoupling). Results of our study, constrained by a high-quality database, exclude fully decoupled mode and favor isostatic compensation level in the asthenosphere. Interpretation of our results in light of geological and geophysical data suggests that the present Valencia Trough is best described by partial lithospheric decoupling. 6 2003 Elsevier Science B.V. All rights reserved.

Relationships Between M w and Other Earthquake Size Parameters in the Spanish IGN Seismic Catalog

An important part of the preparation and homogenization of the seismic catalog used in the recent seismic hazard assessment study of Spain is the development of relationships among the different scales used to measure earthquake size. The objective is to convert all earthquake size data in the original catalog to a single magnitude scale, the moment magnitude Mw, in order to have a set of events with an uniform comparable size measurement. These new relationships are based on regression analysis between Mw and the other units used in the catalog in different epochs. The reduced major axis regression scheme is used, because it is the most suitable method for symmetric treatment of the variables involved in the fits. The new relationships obtained for Spain, Mw as a function of mbLg; Mw as a function of mb; and Mw as a function of Imax, are presented and their applicability limits and accuracy are discussed. The results obtained could have other practical uses in regional seismicity analysis.

Models for reproducing the damage scenario of the Lorca earthquake

A damage scenario modelling is developed and compared with the damage distribution observed after the 2011 Lorca earthquake. The strong ground motion models considered include five modern ground motion prediction equations (GMPEs) amply used worldwide. Capacity and fragility curves from the Risk-UE project are utilized to model building vulnerability and expected damage. Damage estimates resulting from different combinations of GMPE and capacity/fragility curves are compared with the actual damage scenario, establishing the combination that best explains the observed damage distribution. In addition, some recommendations are proposed, including correction factors in fragility curves in order to reproduce in a better way the observed damage in masonry and reinforce concrete buildings. The lessons learned would contribute to improve the simulation of expected damages due to future earthquakes in Lorca or other regions in Spain with similar characteristics regarding attenuation and vulnerability.

Ground-Motion Characterization of Low-to-Moderate Seismicity Zones and Implications for Seismic Design: Lessons from Recent Mw ∼4.8 Damaging Earthquakes in Southeast Spain

We address the ground-motion characterization of three damaging earthquakes that occurred in the low-to-moderate seismicity region of Murcia (southeast Spain) and compare our results with current earthquake-resistant provisions to establish whether those provisions are consistent with the available data or need to be revised. The analyzed series are the 1999 Mula ( m b Lg 4.8, I EMS = VI), the 2002 southwest Bullas ( m b Lg 4.8, I EMS = VI), and the 2005 La Paca ( m b Lg 4.7, I EMS = VII). Recorded peak ground accelerations are low (pga 20 km). We find that local factors control the distribution of ground motions, possibly in combination with propagation effects. Characteristic spectral shapes, representative of ground motions at each station, are observed. Several ground-motion predictive models and a simulation method are used for estimating accelerations and response spectra in the most damaged towns, where no records exist. The different methods consistently predict similar response spectra for the epicentral areas. Recorded and predicted normalized spectral shapes exceed the design spectral shape of the Spanish Building Code ncse-02 for all soil categories for intermediate– high frequencies (above about 3 Hz). Moreover, the ncse-02 absolute response spectra are possibly exceeded by the corresponding predicted spectra for the epicentral areas in the same frequency range. Predominant frequencies of common soils and critical periods of most conventional buildings in the Region of Murcia also lie in this frequency range. These factors could explain, in part, the observed damage. The results raise questions about the definition of the ncse-02 design spectra, and specifically about the design spectral shape used. The approach followed in this work may be used to calibrate other national seismic codes, especially of regions with similar characteristics: moderate seismicity and limited availability of ground-motion data.

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.

Statistical analysis of the 2012–2013 Torreperogil–Sabiote seismic series, Spain

The study of earthquake swarms and their characteristics can improve our understanding of the transient processes that provoke seismic crises. The spatio-temporal process of the energy release is often linked with changes of statistical properties, and thus, seismicity parameters can help to reveal the underlying mechanism in time and space domains. Here, we study the Torreperogil–Sabiote 2012–2013 seismic series (southern Spain), which was relatively long lasting, and it was composed by more than 2000 events. The largest event was a magnitude 3.9 event which occurred on February 5, 2013. It caused slight damages, but it cannot explain the occurrence of the whole seismic crises which was not a typical mainshock–aftershock sequence. To shed some light on this swarm occurrence, we analyze the change of statistical properties during the evolution of the sequence, in particular, related to the magnitude and interevent time distributions. Furthermore, we fit a modified version of the epidemic type aftershock sequence (ETAS) model in order to investigate changes of the background rates and the trigger potential. Our results indicate that the sequence was driven by an aseismic transient stressing rate and that the system passes after the swarm occurrence to a new forcing regime with more typical tectonic characteristics.

Approach for combining faults and area sources in seismic hazardassessment: Application in southeastern Spain

This paper presents a methodological approach for seismic hazard assessment that considers a hybrid source model composed by faults as independent entities and zones (containing the residual seismicity). The seismic potential of both types of sources is derived from different data: for the zones, the recurrence model is estimated from the seismic 10 catalog. For fault sources, it is inferred from kinematic parameters derived from paleoseismicty and GNSS measurements. Distributing the seismic potential associated to each source is a key question when considering hybrid models of zone and faults, which some authors solve by assigning to the fault only the earthquakes that exceed a fixed magnitude value Mc. In the present approach, instead of restricting the magnitudes of each type of source, the distribution of seismic potential is carried out only for magnitudes below the maximum magnitude value completely recorded in the catalog (Mmaxc). This is 15 derived from a completeness analysis and can be lower than the Mmax generated by the faults, taking into account that their the recurrence period can be higher than the observation period of the catalog. The proposed approach is applied in southern Spain, a region of low-to-moderate seismic where faults move slowly. The results obtained are contrasted with the results of a seismic hazard model using the traditional zone model exclusively. Results show a concentration of expected accelerations around fault traces using the hybrid approach, which is not 20 appreciated in the classic approach using zones exclusively.