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H2020

PALEOSEISQUAKE Report Summary

Project ID: 657769
Funded under: H2020-EU.1.3.2.

Periodic Reporting for period 1 - PALEOSEISQUAKE (New approaches in subaqueous PALEOseismology using high‐resolution SEISmics to derive single net paleoearthQUAKEs displacement and to characterize the seismic cycle on active faults)

Reporting period: 2016-08-01 to 2018-07-31

Summary of the context and overall objectives of the project

PALEOSEISQUAKE: New approaches in subaqueous PALEOseismology using high‐resolution SIESmics to derive single net paleoearthQUAKEs displacement and to characterize the seismic cycle on active faults.

Since the beginning of the XXI Century, our society has witnessed the occurrence of the offshore Sumatra (2004) and Japan (2010) earthquakes and subsequent tsunamis, which caused tens of thousands of casualties and extensive and severe damage. These events has shown that understanding the earthquake history of active submarine faults is key to comprehend better the related seismic hazard and, thus, to mitigate the consequences of future events. Accordingly, the study of past earthquakes is essential in modern seismic hazard assessment.

Paleoseismology is a field of research that allows characterizing past earthquakes and determining the seismic potential of source faults based on the interpretation of the geological record. Thus, its strength is that covers much longer periods than the instrumental or historical seismic information. Subaqueous paleoseismology merge and integrate paleoseismology and marine geology to detect and describe the occurrence of paleoearthquakes on faults located underwater. Recent advances in subaqueous paleoseismology have allowed to derive the submarine paleoearthquake records directly on-faults and their individual vertical displacement.

The main objective of the PALEOSEISQUAKE project is to implement a new approach to characterize the seismic potential of active faults, with special emphasis on recognizing single event displacements and obtaining precise slip-rates. To achieve this objective different active fault systems located in the California margin (US) and Alboran Sea (southeastern Iberia) will be analyzed using high-resolution (HR) seismic data to derive 3D geological models where displacements will be calculated. The resulting methodology will give more accuracy on the estimation of the upper Quaternary slip-rates of the faults and improve scientific knowledge about their behavior, but, also, reduce the uncertainties on the data used to estimate the seismic and tsunami hazard in the coastal areas.

PALEOSEISQUAKE is an original and innovative project that aims to develop a new scientific approach using modern analysis techniques, and will represent a step forward in subaqueous paleoseismology.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

PALEOSEISQUAKE is a project devoted to understand better the earthquake history and earthquake characteristics of offshore active faults in the California margin and in the Alboran Sea by means of high-resolution seismic data. The project has been focused in the offshore Ventura basin (VB; California margin) and in the Yusuf Fault (YF; Alboran Sea).

During the first two years of the project I have:

1- Read and compiled information about the California margin and Alboran Sea geology and their geodynamic evolution, as well as about seismic processing and submarine paleoseismology analysis.

2- Received training in seismic processing on 2D HR-CHIRP profiles and HR-multichannel seismic profiles. The processing of the seismic data is essential to carry on the interpretation of the geological structures and the seismostratigraphic units.

3- Interpreted the seismic profiles in the VB and, partially, across the YF. In the VB, two different seismostratigraphic units have been identified that are separated by a regional erosion surface corresponding to the Last Glacial transgression. Several faults and folds deform the seismostratigraphic units. In the YF area, up to five different seismostratigraphic units have been interpreted based on regional information and borehole data. The YF is clearly imaged in depth and offsetting the units.

4- Integrated the information coming from the seismic interpretation as well as other information (e.g., earthquakes, bathymetry or topography) in a GIS software and in a 3D visualization and analysis software in the VB. In the YF, the GIS database is in construction.

5- Development of an approach to identify on-fault paleoearthquakes in thrust faults using HR seismic data and interpreting different growth strata sequences (Fig.1). This approach has been used to establish the Holocene earthquake activity in four fault systems in the VB, where three to four surface deformation events have been determined.

6- Calculation of the vertical uplift related to individual earthquakes and short-term uplift rates based on the HR seismic data and using different approaches. The results show that the active faults in the VB can produce large uplifts (up to 10 m) and then the occurrence of an earthquake in these faults could trigger a tsunami.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

One of the main results of the project has been development of an approach to on-fault identification of paleoearthquakes related to thrust faults (Fig.1) used to determine the paleoearthquakes occurred in different active faults in the Ventura basin (California margin). This zone has been the focus of different studies, but during PALEOSEISQUAKE we have mapped for the first time with high accuracy the offshore active structures and have produce the first onshore-offshore structures correlation. Based on the results of the paleoseismological study, we have determined the occurrence during the Holocene of between 3 and 4 large related to these structures. The vertical uplifts per event range between 1 and 10 m and the Holocene vertical uplift rates between 1 and 2.4 mm/yr. Our results are in agreement with results obtained in onshore paleoseismological studies. In addition, the estimated surface vertical displacements show the potential of these faults to also generate a tsunami during the earthquake rupture. This new information would help to improve seismic and tsunami hazard assessment and to characterize better the hazard level of the areas surrounding the offshore Ventura basin.

On the last year of the project it is foreseen to finish the paleoseismological analysis of the Yusuf fault on the Alboran Sea. This large fault (~ 200 km) shows evidences of upper Quaternary activity. The expected results will contribute to the definition of the 3D geometry of the fault system and to define its recent deformation history. During the interpretation, in addition to the definition of the seismostratigraphic units offset by the faults and its structure in depth, it has been observed the presence of large mass transport deposits on the basin. Some of these deposits has a regional distribution that allows interpreting them as earthquake triggered. This might indicate that the occurrence of a large earthquake could trigger large submarine landslides contributing to the possibility of a tsunami generation. In addition, it will be interpreted a 3D sparker seismic dataset acquired in the Newport-Inglewood-Rose Canyon (NIRC) fault system. The objective is to carry on a study of the sedimentary evolution related to the fault activity through time. The expected results will allow to determine the slip rate on the different faults and the upper Quaternary deformation history. This information will allow a better estimation of the hazard related to the NIRC fault system and the threat that this system represents to populated coastal areas.

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