# Multi-proxy investigations into the active tectonics of the Bokkoya strike-slip fault, southern Alboran Sea

Léa Vidil, E d'Acremont, L Emmanuel, F Caroir, Sara Lafuerza, Sylvie Leroy, G Ercilla, Alain Rabaute, J Galindo-Zaldivar, E M Latni, et al.

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Léa Vidil, E d'Acremont, L Emmanuel, F Caroir, Sara Lafuerza, et al. Multi-proxy investigations into the active tectonics of the Bokkoya strike-slip fault, southern Alboran Sea. Tectonophysics, 2025, 915, 10.1016/j.tecto.2025.230922. hal-05299187

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Distributed under a Creative Commons Attribution 4.0 International License
Multi-proxy investigations into the active tectonics of the Bokkoya strike-slip fault, southern Alboran Sea

L. Vidil<sup>a,*</sup>, E. d'Acremont<sup>a</sup>, L. Emmanuel<sup>a</sup>, F. Caroir<sup>a</sup>, S. Lafuerza<sup>a</sup>, S. Leroy<sup>a</sup>, G. Ercilla<sup>b</sup>, A. Rabaute<sup>a</sup>, J. Galindo-Zaldivar<sup>c,d</sup>, E.M. Latni<sup>e</sup>, A. Guittet<sup>a</sup>, J.F. Brouillet<sup>a</sup>, the Albacore team<sup>1</sup>

ARTICLE INFO

Keywords:

Submarine paleoseismology

Al Idrissi fault zone

Active faults

Sedimentary cores

Sub-bottom profiles

Contourite

A B S T R A C T

In the Alboran Sea, oblique convergence between African and Eurasian plates led to the formation of the active NNE-SSW Al Idrissi sinistral strike-slip fault system ~1 Ma ago, generating several moderate-magnitude earthquakes (Mw > 6). This study investigates the dynamics of this emerging plate boundary by analysing seismic events recorded in sedimentary sequences over the past 120 kyr. A multi-proxy approach combining sediment cores, piezocone tests, multibeam bathymetry, seismic reflection and sub-bottom profiles was applied for the first time to investigate and quantify tectonic activity along the Bokkoya fault. This NNE-SSW-oriented fault system segments the southern part of the Small Al Idrissi Volcano and locally forms a local transtensive basin. These proxies have allowed the identification and dating of faulted sedimentary sequences and major erosive events. An intense erosional period in the western contouritic drift between 90 and 60 kyr is responsible for the strong thickness asymmetry observed between the two blocks of the Bokkoya fault. The vertical displacement history of the north Bokkoya segment reveals a succession of four possible paleoearthquake events preserved since 120 kyr. These are the sum of coseismic events and potential post-seismic slips related to fault creeping or aseismic creep. The studied segment exhibits transtensional deformation and shows a cumulative vertical offset of 33 m, with distinct phases of vertical displacement: a higher rate (0.30 mm yr-1) between 90 and 40 kyr, followed by a general slowdown to 0.17 mm yr-1 since 40 kyr. From a detailed study at the core scale, at least three preserved paleoearthquake events are identified, dated at 42, 21.5, and 17.5 kyr. This study presents the seismic and aseismic behaviour of a segment from the Bokkoya strike-slip fault, providing insights into the mechanisms governing fault activity during the evolution of a nascent plate boundary.

1. Introduction

Earthquakes are a natural hazard with one of the greatest impacts on the world's populations, yet predicting when and where they will occur remains a key challenge. This is because earthquake triggering and the consequent seismic and tsunami hazard potential depend on the interplay of a range of regional and local factors (e.g. stress fields, fault network geometries and physical properties as friction and local physical conditions such as pressure and temperature) (Okal and Synolakis,

2003; Geist and Lynett, 2014; Gràcia et al., 2019; Gómez De La Peña et al., 2022; Estrada et al., 2021) that remain poorly constrained on the same study.

Assessments of future earthquakes and their potential hazard can be enhanced through knowledge of fault segment characteristics and long-term earthquake cycling (Pouderoux et al., 2014). It is generally accepted that (i) the longer the co-seismic fault segments, the greater the magnitude of the earthquakes generated, and (ii) stress accumulation along a fault is proportional to the time elapsed since the previous

<footnote><sup>a</sup> Sorbonne Université, CNRS-INSU, Institut des Sciences de la Terre Paris, ISTE, F-75005 Paris, France</footnote>

<footnote><sup>b</sup> Instituto de Ciencias del Mar, CSIC, 08003 Barcelona, Spain</footnote>

<footnote><sup>c</sup> Instituto Andaluz de Ciencias de la Tierra, CSIC-UGR, Granada, Spain</footnote>

<footnote><sup>d</sup> Departamento de Geodinámica, Universidad de Granada, Granada, Spain</footnote>

<footnote><sup>e</sup> Marine Royale, Division Hydrographie Océanographie et Cartographie (DHOC), Morocco</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>E-mail address: lea.vidil@sorbonne-universite.fr (L. Vidil).</footnote>

<footnote n="1">¹ Albacore Team: d'Acremont E., Lafuerza S., Alonso B., Benmarha O., Besso R., Campderros S., Corbera G., Dano A., De la Fuente M., Latni E.M., Emmanuel L., Estrada F., Frigola J., Gorini C., Ketzer M., Leroy S., Le Roy P., Lopez-Gonzalez N., Oliveira de Sa A, Palomino D., Praeg D., Rabaute A., Scalabrino B., Sheremet Y., Tendero Salmeron V., Vidil Léa</footnote>
earthquake (Wells and Coppersmith, 1994; Hanks and Kanamori, 1979). To obtain probabilistic estimates of the timing and size of future events along a given fault segment, it is necessary to quantify earthquake recurrence characteristics (e.g. Burbank and Anderson, 2001; McCalpin and Carver, 2009). However, faults with slow slip rates show a variety of seismic behaviours, from periodic activity to clustered events alternating with long periods (> kyrs) of seismic quiescence (Crone et al., 1997). In addition, fault deformation is accommodated seismically, by

creep or by a mixed behaviour that involves both seismic slip (abrupt rupture) and aseismic slip (gradual and steady creep) (Wesson, 1988). Quantifying fault behaviour and earthquake cycling thus require access to long, continuous records of sedimentary successions and physical properties that span a statistically significant series of earthquakes. On land or at sea, few sites offer records that are sufficiently long as in Japan, America, or even in New Zealand (e.g. Goldfinger et al., 2007; Sykes and Menke, 2006, Pouderoux et al., 2014; Usami et al., 2018;

<figure><img src="image_2.png" /><figcaption>**Fig. 1.** Active faults and seismicity of the Bokkoya fault system (BF) and Al Idrissi fault system (AI) in the frame of Alboran Sea. (A) Bathymetric of the Alboran Sea showing the structural features. Shaded bathymetry from compilation of ISTEP and CSIC multibeam cruises with GEBCO 2014 database (https://www.gebco.net/), topography from SRTM database. Focal mechanism in orange: 1910 main shock (Stich et al., 2020). Focal mechanism in black: 1994 main shock (El Alami et al., 1998). Focal mechanism in red: 2004 main shock (Van Der Woerd et al., 2014). Focal mechanism in green: 2016 main shock (Buforn et al., 2017; Kariche et al., 2018; Medina and Cherkaoui, 2017). Focal mechanism in grey: 2021 main shock (Henares et al., 2024; Lozano et al., 2025). AF, Averroes Fault; AIFZ, Al Idrissi Fault Zone; AR, Alboran Ridge; BAF, Boussekour-Aghbal Fault; BF, Bokkoya Fault; CSF, Carboneras Serrata Fault; EAB, East Alboran Basin; FP, Francesc Pagès Seamount; JF, Jebha Fault; NB, Nekor Basin; NF, Nekor Fault; SAB, South Alboran Basin; SAR, South Alboran Ridge; TB, Tofino Bank; TF, Trougout Fault; WAB, West Alboran Basin; XB, Xauen Bank; YF, Yusuf Fault. Orange dashed rectangle corresponds to the key study area. The Al Idrissi fault system (AI) and the Bokkoya fault system (BF) are belonging to the AIFZ and the Small Al Idrissi Volcano (SAIV) is acting as a relay between these fault systems. Offshore-onshore main structural features from Crespo-Blanc and De Lamotte, 2006; Martínez-Garcia et al., 2011 and d'Acremont et al., 2020. Inset: Main limit of active faults and red dashed are supposition of limit plate boundary modified from Billi et al., 2023. (B) and (C) Study area with structural features (from Lafosse et al., 2020; d'Acremont et al., 2022) and epip CENTRES OF THE EARTHQUAKES, WITH A MAGNITUDE GREATER THAN 2, RECORDED BETWEEN 1964 AND 2024 (SPANISH INSTITUTO GEOGRAFICO NACIONAL, IGN database). THE DASHED ORANGE RECTANGLE IS THE SMALL AL IDRISSI VOLCANO (SAIV) STUDY AREA. BAIV, BIG AL IDRISSI VOLCANO. (FOR INTERPRETATION OF THE REFERENCES TO COLOUR IN THIS FIGURE LEGEND, THE READER IS REFERRED TO THE WEB VERSION OF THIS ARTICLE.)</figcaption></figure>
Meyer et al., 2025...), i.e. on the order of $10^4–10^5$ years. Fault activity may be reconstructed at high temporal resolution using high-resolution seismic reflection data, from observed changes in sediment thickness (syn-tectonic units) and unit offsets across faults (e.g. Parke et al., 1999; Stefatos et al., 2002). Earthquake activity may also be inferred from proxies observed on sub-bottom profiles and in sediment cores, such as turbidites or homogenites (Beck et al., 2007; Seibert et al., 2024).

By combining a comprehensive set of multiproxy data from both geophysical and geological sources at a single study site in the south of Alboran Sea, this work enhances the understanding of past seismic activity and provides valuable insights for improving seismic risk assessment in the region. The Alboran Sea is a zone of slow ($<$ 5 mm.yr$^{-1}$, DeMets et al., 2015) oblique NNW-SSE convergence between the African and Eurasian (Nubia) plates, which is characterized by a broad distribution of earthquakes (Buforn et al., 2017; Neres et al., 2016; Stich et al., 2020). In such continental collision, context of slow deformation, it is difficult to precisely constrain where elastic energy accumulates, when and how it is released and thus the resulting seismic hazard (Calais et al., 2016). In that sea, slip-partitioning is expressed in a complex distribution of fault segments of differing styles (compressive, extensional, strike-slip or mixed; e.g. d'Acremont et al., 2020; Estrada et al., 2018; Gracia et al., 2019), which make it difficult to precisely delineate the African-Eurasian plate boundary (Koulali et al., 2011). However, moderate earthquakes are mostly concentrated along the NNE-SSW Al Idrissi fault system (AIFS, Fig. 1), a left-lateral strike-slip system that extends 270 km from Spain (Almeria - Adra) to Morocco (Al Hoceima). The AIFS has developed over the last 1–1.8 Ma, in part on pre-existing structures, and is considered to be a unique example of an incipient intracontinental plate boundary (Gràcia et al., 2019; Lafosse et al., 2020) in continental collision zone (Ruiz-Constán et al., 2011). This fault system is currently growing through propagation and linkage of its segments and could develop into an Africa-Eurasia plate boundary fault (Galindo-Zaldivar et al., 2018; Lafosse et al., 2020; d'Acremont et al., 2020). In the last 30 years, three moderate earthquakes ($6.4 > Mw > 6.0$) have occurred along the AIFS or associated fault segments (Calvert et al., 1997; El Alami et al., 1998; Ait Brahim et al., 2004; Tahayt et al., 2009; Galindo-Zaldivar et al., 2018; Lozano et al., 2025; Figs. 1 and 2). To the south and in continuation of the AIFS, the NE-SW Bokkoya fault system segment the Small Al Idrissi Volcano (Lafosse et al., 2020) and joins onshore the sinistral Bousekkour-Aghbal fault (d'Acremont et al., 2014; Lafosse et al., 2017, 2018). Despite recent studies along the AIFS (Henares et al., 2024; d'Acremont et al., 2022; Gràcia et al., 2019; Estrada et al., 2018), the Bokkoya faults characteristics and long-term earthquake recurrence remain poorly constrained.

In this study, we employed geological, geophysical and geotechnical proxies to examine the relative displacements of blocks on either side of a segment of the Bokkoya fault system. These displacements reflect how this fault segment accumulates or releases tectonic energy through seismic events or creeping processes. The objective is to characterize the slip dynamics of this segment, located in the southern part of the inactive Small Al Idrissi Volcano (SAIV), which seems to serve as a relay between the northern section of the Bokkoya fault zone and the southern end of the Al Idrissi fault system (Fig. 1B-C). This multi-proxy dataset collected along a transect perpendicular to the Bokkoya fault system provided a detailed seismostratigraphy, calibrated with identified seismic horizons, piezocone test (CPTu) and sediment core dating. Results from sub-bottom/seismic reflection profiles correlated to core analyses provide essential inputs to assess fault segment behaviour and variation in the fault activity. Various geological and geophysical proxies were used to detect the presence of tectonic events and sedimentation rate variation within the sedimentary successions on the fault zone over a period of 120 kyr – a timescale constrained by the proxies, in order to identify a reconstruction of the fault’s seismic history and its potential hazard.

## 2. Geological and geodynamical settings

The Alboran Sea is the westernmost Mediterranean basin, limited by the Iberia margin to the north and to the south, the North Africa (Moroccan and Algerian margins) (Fig. 1A). Since the late Tortonian, the Alboran basin has undergone tectonic inversion with the development of reverse faults, folds, and the uplift of the basin margins (Martínez-García et al., 2011; Martínez-García et al., 2013; d'Acremont et al., 2020). Recent deformation is mainly localized along the NNE-SSW Al-Idrissi sinistral and NW-SE Yusuf dextral strike-slip fault systems, formed as a result of the frontal indentation of the Africa and Alboran blocks (Lafosse et al., 2020; Lafosse et al., 2017; Estrada et al., 2018).

The Alboran Sea exhibits an important seismic activity, mainly concentrated along the Trans-Alboran Shear Zone (TASZ) (De Larouziere et al., 1988), which is known for occurring at shallow depths (5–20 km) (Medina and Cherkaoui, 2017)). One of the main active faults on the Alboran Sea, belonging to the TASZ is the Al Idrissi sinistral strike-slip fault zone (AIFZ), oriented NNE-SSW. This fault crosses and segments the western sector of the Alboran Ridge (d'Acremont et al., 2022; Gràcia et al., 2019; Lafosse et al., 2020; Martínez-García et al., 2013). Most of the Africa-Eurasia plate convergence in the western Mediterranean Sea over the last 1–1.8 Ma has been partially accommodated by the AIFZ (Fig. 1; Gràcia et al., 2019; Lafosse et al., 2018, 2020). South of the Alboran margin, in the region of the Small Al Idrissi Volcano, the offshore Al Idrissi Fault System (AIF) has been connected to the active Bokkoya fault system, oriented NNE-SSW (Lafosse et al., 2020). The Bokkoya Fault System (BF) is a normal left-lateral strike-slip fault, located at the north-western boundary of the Nekor Basin (Calvert et al., 1997; El Alami et al., 1998; Van Der Woerd et al., 2014; d'Acremont et al., 2014) and is linked to the west by the left-lateral Bousekkour-Aghdal onshore-offshore fault (Fig. 1B, d'Acremont et al., 2014; Lafosse et al., 2017). Studies in the Al Hoceima region of the 1994 and 2004 seismic events, along with structural investigations, support the hypothesis that the Bokkoya fault system extends on land as part of a complex network of buried faults, oriented approximately NNE-SSW (Biggs et al., 2006; Tahayt et al., 2009; Lafosse et al., 2017).

Historically, earthquakes have generated both seismic and tsunami hazards for surrounding coastal areas. The 1522 event of Almeria ($Mw > 6.5$) caused about 2000 casualties (Reicherter and Becker-Heidmann, 2009; Reicherter and Hübscher, 2007). In 2003, the Boumerdès earthquake ($Mw = 6.8$, North Algeria), generated a tsunami that affected mainly the northern Algeria coast around the Boumerdès Province and the Balearic Islands (Sahal et al., 2009; Selva et al., 2021; Gómez De La Peña et al., 2022). Recently, seismicity in the Alboran Sea has become more localized along the AIFS (Buforn et al., 2017; Stich et al., 2020; Sánchez-Roldán et al., 2024; Lozano et al., 2025). GPS data show that the AIFZ concentrates a slip rate of ~3 mm yr$^{-1}$ (Koulali et al., 2011; Stich et al., 2020). In the last 30 years, three moderate earthquakes ($6.4 > Mw > 6.0$) have occurred along the AIFZ, from the Al Idrissi and Bokkoya fault systems (Fig. 1): in 1994, a $Mw = 5.9$ earthquake caused damage in the Al Hoceima region (Calvert et al., 1997; El Alami et al., 1998); in 2004, another $Mw = 6.3$ shock struck Al Hoceima, resulting in over 600 casualties, 2500 injuries and a large number of collapsed houses (Ait Brahim et al., 2004; Stich et al., 2006; Tahayt et al., 2009); and in 2016, a $Mw = 6.4$ earthquake occurred farther offshore (Fig. 1) (Galindo-Zaldivar et al., 2018). Since 2021, a sequence in southern Alboran started mid-April 2021 and persisted more than 36 months (Lozano et al., 2025). This seismic crisis has been ongoing to the east of the fault system in the area of the Big Al Idrissi Volcano (BAIV), with a major event of magnitude 5.3 and 5.5 in 2022 (Fig. 1B) (Lozano et al., 2025; Bouhali et al., 2025; Spanish Instituto Geografico Nacional, IGN database).

The deep sea in the Alboran basin is widely driven by the oceanographic circulation of Atlantic Water (AW) and Mediterranean Waters (MWs), inducing contouritic processes that have shaped the seafloor since the opening of the Strait of Gibraltar (Ercilla et al., 2016; Juan et al., 2016, 2020). Bottom currents of these water masses create a
complex seafloor morphology, which influences the transport, sedimentation, reworking and erosion of near-surface sediments, leading to the formation of contourite sedimentary reliefs (Ercilla et al., 2016, 2021) (Figs. 1A and 2). The topographic highs control the water masses circulation and geometry of contouritic systems (Juan et al., 2016; Lafosse et al., 2020; d'Acremont et al., 2020) (Figs. 2, inset). To the south of the Alboran Ridge, close to the AIFZ, bottom-currents of the Western Mediterranean Deep Water (WMDW) are steered by the presence of structural highs (Francesc Pagès, Small Al Idrissi Volcano and Big Al Idrissi Volcano) (Fig. 2). The interaction between these structural highs and bottom-currents leads to the formation of contourite systems with presence of moats and drifts (confined and plastered, Fig. 2 inset) (Ercilla et al., 2016; Juan et al., 2020). The presence of the circular Small Al Idrissi Volcano (SAIV) and its morphological segmentation by the Al Idrissi and Bokkoya fault systems cause changes in seafloor topography that lead to alterations in the speed and direction of the WMDW bottom currents and consequently, the resulting contourite systems (Fig. 2, inset). The SAIV is considered as an inactive volcano since the Pliocene (4.5–5.33 Ma), with a 4–5 km wide conic structure, roughly trending NNE-SSW (Lafosse et al., 2020). This structural high seems to have shifted due to the presence of the sinistral strike-slip active faults (Lafosse et al., 2020) (Fig. 2).

# 3. Material and methods

## 3.1. Geophysical data

The dataset includes swath-bathymetry and seismic reflection profiles that were acquired during the oceanographic survey ALBACORE (d'Acremont and Lafuerza, 2021) onboard the R/V "Pourquoi Pas?". The swath-bathymetry was acquired with a multibeam echosounder (SMF) ©RESON-Seabat 7150 bi-frequency 12/24 kHz, allowing the acquisition of swath-bathymetry with a 20 × 20 m resolution grid. The very high-resolution sub-bottom profiles were acquired with a sub-bottom sediment sounder Chirp 1500–6500 Hz, ranging from 10 to 100 ms (Ixblue PWM) along the multibeam bathymetry surveys of ALBACORE cruise with 50 m approximate depths of investigation. The signal frequency varied between 6500 and 1500 Hz, allowing for ~100 m penetration in soft sediments with an average vertical resolution of 0.25 m. We will use the term *sub-bottom profile* when referring to sub-bottom profiler data. Seismic reflection profiles are also used in this study including 2D seismic reflection profiles acquired during the Marlboro-1 and SARAS surveys (d'Acremont 2011; 2012), using a multi-channel airgun system yielding 5 m of vertical resolution (750 m approximate depths of investigation) and a single-channel SIG sparker system with 1 m of vertical resolution (200 m approximate depths of investigations), respectively (d'Acremont et al., 2014; Lafosse et al., 2017, 2020).

The Vp values used for depth conversion from the seafloor to depth are derived from an average value of propagation velocity of 1500 m·s⁻¹ (P-Wave propagation data from MSCL core logger of this study), used to convert the sub-bottom profiles into depth meters and estimate the units' thicknesses and the vertical fault throws along the faults. The uncertainties used for the vertical throws and the unit thicknesses were calculated with ±50 m·s⁻¹ and with the average vertical resolution of 0.25 m from seismic data.

The seismic data were interpreted using Kingdom IHS Suite© software, while maps were created using ArcGIS Pro© software. The sub-bottom profile dataset was employed to delineate seismic horizons and units, to analyse sedimentary units, deformation styles, and the spatio-temporal evolution of tectonic structures. Seafloor morphology was examined using swath-bathymetric data to identify surface expressions of tectonic features. Faults were identified based on sediment horizon offsets observed in the sub-bottom profiles and on the seafloor. A reliable correlation of reflectors between the western and eastern compartments was performed using the intersections between sub-bottom profiles (inset, Fig. 3).

<figure><img src="image_3.png" /></figure>

**Fig. 2.** Bathymetric map showing topographic structural highs, fault systems, the location of sub-bottom sediment sounder (PP0), air-gun (MAR14) and SPARKER (SARAS) sources sub-bottom profiles, cores and CPTu data studied in this paper. The red lines are the normal and strike-slip faults affecting the seafloor identified from swath-bathymetry data (modified from Lafosse et al., 2017 and Lafosse et al., 2020). AIF, Al Idrissi fault; BAIV, Big Al Idrissi Volcano; BF, Bokkoya fault; FP, Francesc Pagès; SAIV, Small Al Idrissi Volcano; TB, Tofino Bank; WMDW, Western Mediterranean Deep Water. Inset: close-up view of the SAIV, zoom on the SAIV with moat around the topographic high; plastered drift and confined drift at the southern and northern parts of the volcano, respectively. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

## 3.2. Sediment cores

Time calibration of seismic horizons and units, as well as measurement of sedimentation rates, is based on two calypso piston cores, ALB_CL26 and ALB_CL54. Cores sediments were carried out on a transect perpendicular to the northern fault segment from the Bokkoya fault system. (Table 1, Figs. 2 and 3). These cores penetrated 10.8 m and 17.9 m, respectively (corrected core length). The core ALB_CL26 is located at the western contourite drift, on the western fault block (Fig. 3). The core ALB_CL54 is located very close to the active strike-slip Bokkoya fault, in the depression zone, between the contourite drifts (Table 1, Fig. 3). Both locations are currently swept by the WMDW (Western Mediterranean Deep Water) (Ercilla et al., 2019), and the sedimentary units are affected by the active Bokkoya strike-slip fault. Dating and isotopic analysis results were used to help correlation with the other proxies as seismic horizons, CPTu data, gamma density and lithology of the cores.

The sampled core lengths were corrected to obtain the most accurate depths using IFREMER's CINEMA software, based on accelerometer measurements obtained during coring (Badhani et al., 2020) and by comparing physical parameters (MultiSensor Core Loggers, MSCL) from other smaller Calypso piston and gravity cores in the same location (d'Acremont and Lafuerza, 2021, also see supplementary materials 7.1).

## 3.3. In-situ geotechnical measurements (CPTu)

In-situ geotechnical measurements were carried out during the ALBACORE cruise, using the Ifremer piezocone (CPTu) PENFELD, developed by IFREMER (Sultan et al., 2007). The CPTu is used to characterize sediment mechanical properties and lithology at water depths up to 6000 m (Sultan et al., 2010). The tool consists of a continuous rod that penetrates sediments continuously (2 cm·s⁻¹) up to 50 m below the seafloor (mbsf), providing measurements of the tip resistance (qc), sleeve friction (fs) and excess pore pressure (Δu2). The tip resistance was corrected (qt) for the unequal area effect (decreased resistance due to the excess pore pressure induced by the cone during the test, Lunne et al., 1998; Lunne et al., 2002) (qt), CPTu PENFELD leads to greater
<table><caption>**Table 1**

List of cores analyzed during the ALBACORE cruise along the PP0130 sub-bottom profile.</caption><thead><tr><th>Core name</th><th>Latitude</th><th>Longitude</th><th>Water depth (m)</th><th>Core length (m)</th><th>Corrected core length (m)</th></tr></thead><tbody><tr><td>ALB_CL26</td><td>N35.4166°</td><td>W3.7841°</td><td>412</td><td>10.03</td><td>10.8</td></tr><tr><td>ALB_CL54</td><td>N35.41621°</td><td>W3.7814°</td><td>427</td><td>16.04</td><td>17.9</td></tr></tbody></table>

accuracy and sensitivity measurements in soft sediment (Lafuerza et al., 2008).

PENFELD tests were run to correlate precisely seismic reflection data with cores and provide an architectural model of the sedimentary succession affected by fault activity. This article focuses on one parameter (qt) for stratigraphic purposes. Several examples of the stratigraphic application of CPTu data exist in the literature (Robertson, 1990; Lunne et al., 2002; Amorosi and Marchi, 1999; Robertson, 2009; Lafuerza et al., 2008).

For this study, five PENFELD tests (PF05–01, PF05–03, PF05–04, PF05–05, PF05–06) were carried out along the sub-bottom profile PP0130, which was converted to depth and flattened according to the seafloor to facilitate correlations (Fig. 8). CPTu data enable the detection of variations in soil resistance (qt) up to 40 m in depth (Fig. 8). Here a filtered qt has been selected for correlations with seismic data, filtered qt values correspond to the removal of noise in order to highlight significant values and help the correlation with other proxies.

### 3.4. Chronostratigraphic analysis and age model

The combined use of ¹⁴C and variations of δ¹⁸O of planktonic foraminifera enables the establishment of a reliable chronostratigraphy of marine sediments. Oxygen isotope analyses in combination with AMS radiocarbon dating, allow us to identify the magnitude of any hiatuses within the sedimentary record up to the analytical limit of AMS (~43 kyr). Past this age limit, oxygen isotope analyses cannot provide sufficient temporal resolution to identify the magnitude of hiatuses. However, it has been possible to characterize the Marine Isotope Stages (MIS) through comparison to other isotope records from the same area.

Samples collected for chronostratigraphic analyses were picked from hemipelagic layers along cores. The collection for δ¹⁸O isotope analysis was as systematic as possible, with a depth interval ranging between 5 cm for core ALB_CL54 and 10 cm for core ALB_CL26. Bulk samples were sieved by washing over 63 µm and 150 µm stainless steel sieves. No chemicals were used to disaggregate the sediments and at all stages in

the processing, de-ionized water was used to ensure no dissolution of the carbonate microfossils. Both fractions were collected and gently dried in an oven at 40 °C for 24 h.

Monospecific pristine tests of planktonic foraminifera *Globigerina bulloides* were hand-picked (3–5 specimens per sample – carbonate weight between 50 and 100 µg) from the size fraction >150 µm for stable oxygen isotopes analyses (δ¹⁸O) on the cores available along the sub-bottom profile (ALB_CL26, ALB_CL54). Samples were reacted with 100 % H₃PO₄ acid under vacuum in a Kiel IV automatic preparation device at 70 °C, and the resulting CO₂ was analyzed using a coupled ThermoFisher Delta V Advantage IRMS mass spectrometer. Oxygen isotope (δ¹⁸O) measurements were carried out by isotope-ratio mass spectrometry (IRMS) at IStEP laboratory, Sorbonne University (Paris - France). Isotope values (δ¹⁸O) are reported as per mil (‰) deviation of the isotopic ratios (¹⁸O/¹⁶O). The analytical precision of the laboratory standards is up to 0.06 ‰ for δ¹⁸O. Calibration to Vienna Pee Dee Belemnite (VPDB) was performed by means of NBS-19 international standard (Coplen, 1996).

The chronology of ALB_CL26 and ALB_CL54 cores was also constrained by Accelerator Mass Spectrometry (AMS) ¹⁴C data. For ¹⁴C dating, approximately 10 mg of mixed species of planktonic foraminifers of a size >150 µm were picked from each of the selected hemipelagic sediment layers. AMS analyses were performed by the ARTEMIS National Platform at the LMC14 laboratory (CEA Saclay, Gif sur Yvette, France) using their in-house protocols. N samples were selected from the upper 10 m of Core ALB_CL54, and seven samples from the upper 7 m of core ALB_CL26. Radiocarbon dating results are reported in Table 2) as conventional radiocarbon years BP, expressed at the ±1σ level for overall analytical confidence. The AMS dates are calibrated against the Marine20 dataset (Heaton et al., 2020) set using Calib 8.2 Radiocarbon Calibration Software (Stuiver and Reimer, 1993). The chronology of the lower part of the different cores is based on the correlation of planktonic foraminifera *Globigerina bulloides* oxygen isotopic record (δ¹⁸O) with other records from the Alboran Sea, i.e. IODP Site 977 (Martrat et al., 2004).

### 3.5. Submarine paleoearthquake records

On-fault submarine paleoearthquake records can be derived from high-resolution seismic reflection profiles (e.g. Barnes and Pondard, 2010) and sediment cores. In order to estimate the coseismic characteristics of the fault segments, high-resolution sub-bottom profiles enable the identification of vertically stacked syn-tectonic units and horizons shifted vertically by a normal fault. The sites measuring the

<figure><img src="image_4.png" /><figcaption>**Fig. 3.** Sub-bottom profile PP0130, south of the Small Al Idrissi Volcano (SAIV) (see location in the Fig. 2). Locations of two long pistons cores uncompacted (ALB_CL26, ALB_CL54) and the geotechnical CPTu along the profile (PF05–01, PF05–03, PF05–04, PF05–05, PF05–06) that were used for this study. The inset is showing the location of the sub-bottom profiles available for the correlation.</figcaption></figure>
<caption>**Table 2**</caption>

AMS $^{14}$C radiocarbon of bulk planktonic foraminifer samples from core ALB_CL54 and ALB_CL26. Calibrations from Suiter and Reimer (1993). Dataset Marine20; $^{14}$C Delta R (mean): −17 for ALB_CL54, +35 for ALB_CL26 (CALIB Rev. 8.2 radiocarbon calibration program 2020).

<table><thead><tr><th>Core, lab. Code</th><th>Foraminifer type</th><th>Depth (mbsf)</th><th>Corrected depth (mbsf)</th><th>AMS <sup>14</sup>C age (yr BP and error age BP)</th><th>Calendar age (cal. Years BP)</th><th>Calendar age (cal. Kyr BP)</th></tr></thead><tbody><tr><td>ALB-CL54-1-19/21</td><td>Bulk planktonic</td><td>0.20</td><td>1.2</td><td>620 ± 30</td><td>110</td><td>0.1</td></tr><tr><td>ALB-CL54-2-59/61</td><td>Bulk planktonic</td><td>1.60</td><td>2.9</td><td>4030 ± 30</td><td>3895</td><td>3.9</td></tr><tr><td>ALB-CL54-3-79/81</td><td>Bulk planktonic</td><td>2.80</td><td>4.7</td><td>8580 ± 30</td><td>9052</td><td>9.0</td></tr><tr><td>ALB-CL54-4-59/61</td><td>Bulk planktonic</td><td>3.60</td><td>5.4</td><td>12,825 ± 45</td><td>14,454</td><td>14.5</td></tr><tr><td>ALB-CL54-6-09/11</td><td>Bulk planktonic</td><td>5.10</td><td>6.9</td><td>15,120 ± 60</td><td>17,509</td><td>17.5</td></tr><tr><td>ALB-CL54-7-39/41</td><td>Bulk planktonic</td><td>6.40</td><td>8.1</td><td>16,510 ± 60</td><td>19,041</td><td>19.0</td></tr><tr><td>ALB-CL54-8-09/11</td><td>Bulk planktonic</td><td>7.10</td><td>8.8</td><td>17,710 ± 60</td><td>20,498</td><td>20.5</td></tr><tr><td>ALB-CL54-10-04/06</td><td>Bulk planktonic</td><td>9.05</td><td>10.6</td><td>18,520 ± 70</td><td>21,532</td><td>21.5</td></tr><tr><td>ALB-CL54-11-09/11</td><td>Bulk planktonic</td><td>10.10</td><td>11.7</td><td>23,150 ± 100</td><td>26,562</td><td>26.1</td></tr><tr><td>ALB-CL26-1-09/11</td><td>Bulk planktonic</td><td>0.10</td><td>0.4</td><td>1920 ± 30</td><td>1290</td><td>1.3</td></tr><tr><td>ALB-CL26-3-29/31</td><td>Bulk planktonic</td><td>2.30</td><td>2.6</td><td>6900 ± 45</td><td>7154</td><td>7.1</td></tr><tr><td>ALB-CL26-3-94/96</td><td>Bulk planktonic</td><td>2.95</td><td>3.2</td><td>8860 ± 40</td><td>9309</td><td>9.3</td></tr><tr><td>ALB-CL26-4-24/26</td><td>Bulk planktonic</td><td>3.25</td><td>3.5</td><td>16,090 ± 80</td><td>18,536</td><td>18.5</td></tr><tr><td>ALB-CL26-5-49/51</td><td>Bulk planktonic</td><td>4.50</td><td>4.8</td><td>21,780 ± 150</td><td>25,110</td><td>25.1</td></tr><tr><td>ALB-CL26-6-24/26</td><td>Bulk planktonic</td><td>5.25</td><td>5.5</td><td>30,550 ± 410</td><td>34,157</td><td>34.1</td></tr><tr><td>ALB-CL26-7-24/26</td><td>Bulk planktonic</td><td>6.25</td><td>6.5</td><td>37,450 ± 940</td><td>41,108</td><td>41.1</td></tr></tbody></table>

vertical displacements where chosen close to the fault, avoiding inclined areas or deformed zones. In some cases where the fault zone shows synformal horizons, with short wavelengths, displacement is measured by projecting the gently dipping horizons onto the faults (standard geometric methods Barnes and Pondard, 2010; Barnes and Nicol, 2004; Bull et al., 2006).

The hypothesis of Barnes and Pondard (2010) suggests that coseismic increments can be preserved in the architecture of the sedimentary fill sequence, provided there is sufficient sedimentation. When the fault moves, the vertical displacement of one block relative to the other creates an accommodation space. Sediments accumulate in this depressed area, leading to an increased stratigraphic thickness. During the long-term, interseismic phase, sediments deposited above the syn-tectonic series will have a uniform thickness. This is the case when the sedimentation rate is greater than the fault vertical displacement rate. In this scenario, periodic fault escarpments separated by syn-tectonic sequences will provide excellent preservation of paleoearthquakes. On the other hand, if the vertical displacement rate exceeds the sedimentation rate, the fault scarp persists. Barnes and Pondard (2010) state that the presence of a permanent fault scarp leads to poor to no preservation of paleoearthquakes. No uniformly thick sequences were deposited during the interseismic period because the fault vertical displacement rate is higher than the sedimentation rate. The classic sequence of successive fault growth does not allow for dating specific earthquakes events through the magnitude of coseismic vertical displacements. However, it helps highlight periods when fault dynamics changed, particularly, when high slip rates may indicate the occurrence of potentially larger earthquakes during these periods. The representation of cumulative vertical displacements over time reveals abrupt variations in displacement rates. These variations represent major cumulative seismic events (Barnes and Pondard, 2010). Over multiple seismic cycles, the ratio of horizontal to vertical displacements at a given site may not be constant, and some small vertical displacements may have been associated with significant horizontal displacements at the same sites (Barnes and Pondard, 2010).

Given that fault slip involves both horizontal and vertical movements, the vertical displacements used to estimate paleoseismicity are considered minimal estimates of net slip per cumulative event. Additionally, we selected a site that clearly exhibited a major vertical displacement component.

## 4. Results

The study area is dominated by the Small Al Idrissi Volcano (SAIV), which is a submarine structural high. This inactive volcano is segmented by two fault systems: the Al Idrissi fault system to the north and the

Bokkoya fault system to the south. Focusing on the southern area of the SAIV, the morpho-structural analysis of the submarine high allows us to quantify the strike-slip motion along the Bokkoya fault. Seismic stratigraphy and correlation with multi-proxy data are used to gain further insight into the area's geological features. To quantify the fault's activity over time, an age model and sedimentation rate are calculated. Finally, the fault's past seismic activity and its cyclic behaviour are assessed using the methodology outlined by Barnes and Pondard (2010), providing a clearer understanding of the fault's historical earthquake activity.

### 4.1. Morpho-structural characteristics of the Small Al Idrissi Volcano region

Structural highs and geomorphological features are imaged on the new bathymetric map (Figs. 1B and 2). Structural highs such as Francesc Pagès (FP), Tofiño Banks (TB), Big Al Idrissi Volcano (BAIV) and the southern part of the Alboran Ridge (AR) present abraded surfaces at their summits, forming plateaus about 110 m below sea level (mbls) (Fig. 2). The summit of the Small Al Idrissi Volcano (SAIV) is deeper (230 mbls) and rugged. The SAIV region image also sedimentary con-touritic features (drifts and moats) (Fig. 2, inset). The northern part of the SAIV is considered as *confined drift* and the southern part, as *plastered drift*. Erosional feature as "moat" is present at the base of the SAIV (Fig. 2, inset) (Juan et al., 2020).

To assess the extent of Small Al Idrissi Volcano at depth, seismic reflection data were used. Lower-frequency seismic reflection profiles (sparker and air gun sources) provide deeper information than very high-frequency sub-bottom sediment profiles (Fig. 4). On seismic reflection profiles, the top of the SAIV is characterized by a high-amplitude reflector (Figs. 4C and D). In Fig. 4B and D, the magmatic basement is characterized by chaotic facies, and the volcano's boundary is visible by contrasted high-frequency reflectors from well-bedded sedimentary series. The SAIV magmatic basement is also characterized by high-amplitude reflectors and chaotic facies but also by transparent seismic facies in sub-bottom sediment profile (Figs. 5 and 6). The magmatic basement appears in the subsurface in the western part, with a very thin layer of sediment deposited on top (Fig. 4D and E), both at the surface and at depth, sub-bottom profile illustrates the extent of the SAIV (Fig. 4).

The Small Al Idrissi volcano (SAIV) has an ellipsoidal shape, measuring 8 km in length and 5 km in width at its seafloor outcrop, with an NNE-SSW orientation (Fig. 4A). It rises 300 m from the seafloor to its highest point.

The slopes of the SAIV are steeper on its SSE edge. The presence of moat due to erosional processes by deep bottom currents, partly explains
<figure><img src="image_5.png" /><figcaption>**Fig. 4.** Extent of the Small Al Idrissi Volcano (SAIV) in depth. (A) Map of the depth to the top magmatic basement of the SAIV with simplified structural features of AIFS and BFS, locations of seismic reflection air gun MAR14 and SPARKER SARAS-P07 profiles shown in B and D. Contours of the magmatic basement isobaths are drawn every 100 ms. (B) Seismic reflection profile MAR14 without interpretation. (C) MAR14 sub-bottom profile interpreted, dashed and colored lines are the stratigraphic surface defined and modified from Lafosse et al., 2020. The sub-bottom profile shows the extent at depth of the SAIV magmatic basement. Exaggeration Vertical, VE = 8 @ 1500 m·s⁻¹. (D) Seismic reflection profile SARAS-P07 without interpretation. (E) Interpreted SARAS-P07 profile with the SAIV magmatic basement, Bokkoya strike-slip faults, and reflectors identified in other sub-bottom profiles from the ALBACORE cruise. Vertical exaggeration, VE =12 @ 1500 m·s⁻¹.</figcaption></figure>

the morphology of the seabed, particularly in the eastern and southwestern parts of the volcano (Fig. 4A and D). The magmatic body appears to be segmented and displaced by the NNE-SSW faults with sinistral strike-slip components (Figs. 4 and 6). The SAIV is segmented and displaced by the Bokkoya fault system in the south and the Al Idrissi fault system in the north (Figs. 1B and 2). The Bokkoya strike-slip fault, affects the seabed (Figs. 4 and 5a). According to the top-basement map, the magmatic basement has been displaced horizontally from its initial position by 3 km due to the Al Idrissi and Bokkoya fault systems (Fig. 4A).

On the bathymetric map, the traces of strike-slip faults are clearly visible on the seafloor (Fig. 2). The Al Idrissi Fault System is located in the northern part of the volcano, extending over 18 km in a N005°E direction. Deformation from this sinistral strike-slip fault system appears to be distributed as it approaches the SAIV (Fig. 2). In contrast, the southern part of the volcano is crossed by the Bokkoya Fault System, oriented N010°E, which extends for 20 km and reaches the Moroccan coast, exhibiting well-marked relay faults on the seafloor (Fig. 2). At the foot of the SAIV, over 3 km and with an orientation of N010°E, the Bokkoya fault system exhibits two fault segments with local tension. Strike-slip and normal faults show a minimum of vertical fault throw up to 0.75 m (± 0.75 m), visible on seafloor. Both Al Idrissi and Bokkoya fault systems segment and displace the volcano, acting as a relay, as seen in the bathymetric map (Fig. 2) and sub-bottom profiles (Figs. 4, 5 and 7). The offset of the volcano indicates a left-lateral shear component with an apparent horizontal displacement of 3 km, determined by the extent and apparent offset of the magmatic basement (Figs. 2 and 4). Some segments of the Bokkoya fault system exhibit a normal component displacement, particularly in the segment

intersected by sub-bottom profile PP0130 (Fig. 5).

A depression zone, parallel to the fault direction, is identified on the bathymetric and seismic reflection data (Figs. 3 and 5). The sinistral Bokkoya strike-slip fault is observed disturbing the seafloor reflector, revealing dissymmetry between eastern and western sides with western upthrown and eastern downthrown blocks (Fig. 5). Chaotic to transparent facies in depth, correspond to the extent of the SAIV magmatic basement (Sub-bottom profile PP0240 (Fig. 7A). This magmatic body is interpreted as shifted toward the southwest on the western side of the Bokkoya strike-slip fault.

Magmatic basement with chaotic facies deepening southward are also observed (Fig. 7B). The sediment deposits present some erosional truncation (toplap, Units 8 to 4). Units U5 and U6 have been eroded above a buried magmatic high (Fig. 7B). Additionally, offsets along faults are identified in the sedimentary series. These faults are sealed by the U5 unit' base H5, U8, unit's base H8 except for the southernmost one near the Bokkoya fault segment, which is sealed by U2, the unit base H2 (Fig. 7B).

## 4.2. Late Quaternary seismic-stratigraphy near the northern Bokkoya fault segment

The description of the seismic units, along with the reflectors defining their base and top, is provided in Fig. 6, with a zoomed-in view at the sediment core scale shown. The correlation of reflectors between the eastern and western compartments has been confirmed through the intersection of available sub-bottom profiles (Fig. 3). Age calibration of the reflectors and their correlation across the fault were achieved using all available proxies, including lithology, gamma density, isotope data,
radiocarbon dating (¹⁴C), and CPTu measurements at core scale and average sedimentation rate for the deep units (Fig. 5).

### 4.2.1. Seismic units

Based on seismic facies and discontinuities and their correlative continuity surfaces, nine seismic boundaries (Reflectors, H1 to H9) that correspond to the base of each units U1 to U9 and the unit U10 is also identified (Fig. 5). A marked asymmetry of the seismic units is observed on either side of the main Bokkoya Fault, characterized by distinct seismic facies and variations in unit thicknesses, with all units (U1 to U9) being thinner (or absent) on the western side (Figs. 5 and 6).

Multiple datasets, including core samples, intersected sub-bottom profiles (Figs. 4, 5 and 6), as well as zoomed-in sub-bottom profiles

(Figs. 4 and 6), enabled the characterization of seismic facies and were instrumental in establishing a reliable correlation across the study area.

For Unit 1 (U1), both sides exhibit low-amplitude seismic facies. Units 2 and 3 (U2 and U3) are nearly.

undetectable on the western side, whereas the eastern side shows U2 with medium amplitude and low frequency and U3 with low amplitude and medium frequency (Fig. 6). The base of Units 1 and 3 (H1 and H3) are identified with coarser sediments according to gamma density, lithology and CPTu. The unit base H2 is marked with higher impedance on the sub-bottom profile, with coarser sediment and density on ALB_CL54 not visible on the core ALB_CL26 (Fig. 5).

Unit 4 presents high-amplitude, high-frequency signals on the eastern side, while the western side shows a thinner series of high-

<figure><img src="image_6.png" /><figcaption>**Fig. 5.** Top: Interpreted sub-bottom profile. Reflectors (H1 to H9) correspond to bottom horizons, base of each units (U1 to U9), hand-picked units. Nine units were identified (U1 to U9). The red line corresponds to Bokkoya main active strike-slip fault. The red dotted lines are identified as faults. Vertical exaggeration, VE = 9.4. @ 1500 m·s⁻¹. Solid vertical black lines are locations of crossing profiles with the calibration of the intersecting horizons.</figcaption></figure>

Bottom: Zoom on the fault zone of the sub-bottom profile, depth-migrated at 1500 m·s⁻¹, flattened with seafloor horizon, showing the depth correlation of the different available proxies. A stratigraphic log of the two cores (ALB_CL26 and ALB_CL54) with piezocone CPTu data (darker blue curve), gamma density (red curve), and the isotopic δ¹⁸O (blue curve) with red stars, corresponded to ¹⁴C AMS calibration dates, help for a strong correlation and datation of each reflector on a flattened with seafloor horizon. Note that the seafloor is shifted (0.75 m) before flattening by the main Bokkoya fault. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
<figure><img src="image_7.png" /><figcaption>Fig. 6. The tables present the identified seismic units and facies detailed from the West and the East from the sub-bottom profile PP0130. On each side of the drift side, the seismic stratigraphy is different. The base of the units (horizons H1 to H8) were dated with AMS $^{14}$C radiocarbon (in red), with $\delta^{18}$O (in blue) and in black, ages estimated from $\delta^{18}$O using a constant sedimentation rate constrained by cores data up to 30 cm.kyr$^{-1}$. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

amplitude, low-frequency signal. This unit present a series of well-stratified reflectors, coarser sediments, higher gamma density and resistance from CPTu on both cores (Figs. 5 and 6).

Unit 5 exhibits different seismic facies on the western side, where the upper half is transparent and the lower half features medium-amplitude reflectors with medium frequency. Unit 6 is not present on the western side. On the eastern side, Units 5 and 6 are both characterized by low amplitude and low frequency. Unit 6 is characterized at its base by two high-amplitude reflectors (Fig. 6).

Unit 7 is a thin layer observed in the centre of the western compartment. On the eastern side, it is marked by two high-amplitude reflectors at the base of the unit. Unit 8 displays a variation between transparent facies and low-amplitude, low-frequency facies (Fig. 6).

For Unit 9, the western side exhibits low amplitude, transparent facies in the centre and a series of medium-amplitude reflectors on its edges. Strong acoustic anomalies appear on the western side but not on the eastern side. On the eastern side, Unit 9 is characterized by transparent facies with some moderate-amplitude reflectors. The boundaries between the Units 9 and 10 and the SAIV magmatic basement, are not well-defined due to the low penetration of the sub-bottom profiles (Fig. 6).

### 4.2.2. CPTu correlation with seismic-stratigraphy

The ten units (U1 to U10) and nine boundaries (seismic horizons H1 to H9) were plotted on the CPTu data (Fig. 8). Correlation with the sub-bottom profile reveals that filtered qt peaks (> 200 kPa) correlate with seismic horizons H1, H4, H5 and H7. The correlation may differ when seismic units (U2 and U3) are thinner and have lower amplitudes, which results in seismic horizons (H2) having lower acoustic impedance (Figs. 5 and 8). This is illustrated by dotted lines, which indicate uncertain calibration with sub-bottom profile and in-situ data due to a lack of information on both (H3 western side in Fig. 8).

A dissymmetry between the western and eastern fault compartment is registered in CPTu data in line with the sub-bottom profile (Fig. 8). PF05-01 and PF05-03 are both located on the western side of the main fault, with PF05-03 being closer to the main fault (Figs. 5 and 8). PF05-05 and PF05-06 are located on the eastern side, the first being in the depression zone of the faults. Generally, CPTu measurements show good correlations between filtered qt and seismic units, as described here:

In all sites, Unit 1 (H1, orange) is identified by a slight peak in resistance around 3 m depth in the western side and 4.5–5 m in the eastern one (Fig. 5). Seismic horizon H2 is calibrated using variations in seismic facies (Fig. 5), with no significant change in filtered qt on the dynamic penetrometer profiles is observed (Fig. 8). The reflectors (unit's base) were calibrated and correlated in time from core data and with intersected sub-bottom profiles (Fig. 5).

From the sub-bottom profile, the base of Unit 2 (H2) is identified at 5 m on the western side, around 7.5–8 m in the fault zone, and around 7 m on the eastern side. H3 (base of Unit 3, blue) corresponds to the top of Unit 4, which shows no filtered qt variations. On the western side of the main fault, the base of Unit 3 is identified at 7 m, while in the fault zone (PF05-04, PF05-05) and eastern side (PF05-06), the seismic horizons are identified at 12.5, 12 and 11 m respectively (Fig. 8).

Unit 4 (green) is marked by a noticeable increase in filtered qt in the west of the fault (values between 200 and 500 kPa, Fig. 8) in agreement with a more pronounced acoustic impedance on the sub-bottom profile (Figs. 5 and 6). This is observed in the middle part of Unit 4 on the western side compared to the eastern side, where Unit 4 is progressively more resistant downwards.

Unit 5 (purple) exhibits an increase in filtered qt toward the top unit. The base of the unit (H5) is identified at 10 m on the western side, 27.5, 23 and 20 m from the main fault to the eastern side (Fig. 8).

Unit 6 (H6, unit base in brown) is only present on the eastern side and is characterized by high filtered qt (> 500 kPa), mostly in the upper half. The seismic horizon is identified below seafloor depth at 32.5, 29 and 25 m from the main fault to the eastern side, respectively (Fig. 8). On the western fault compartment, the lack of Unit 6 at around 10 m depth below the present-day seafloor suggests it was either eroded or not deposited. Thus, the above and below units (U5 and U7) are bounded by erosional surfaces at both their top and base, which are clearly visible on the sub-bottom profile and filtered resistance (Figs. 5 and 8).

Unit 7 (H7, unit base in light pink) on the eastern side is characterized by alternating intervals of low and relatively high filtered qt peaks (200–500 kPa). This unit is very thin in PF05-03 (~50 cm), thus very difficult to distinguish by CPTu, but can be detected westward by minor variations in PF05-01. From the sub-bottom profile, the depth of the horizon (H7) is identified at 11 m on the western side. In the eastern compartment, the seismic horizon is identified at 40, 35 and 31 m from
<figure><img src="image_8.png" /><figcaption>**Fig. 7.** Sub-bottom sediment profiles showing the Late Quaternary stratigraphy and structural features. The location of profiles is defined in Fig. 2A and inset. Colored lines are reflectors identified with a higher impedance. Units are identified in different colors that seal faults and show the extent in depth of the SAIV magmatic basement. Red area above the SAIV magmatic basement that has disturbed seismic signal. The seismic line PP0240 has a vertical exaggeration of 15 and PP0244 of 13 @ 1500 m·s⁻¹. The black line corresponds to the 450 m area, which shows no unit variations relative to the strike-slip movement. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

the fault toward the east (Fig. 8).

Unit 8 (dark green) exhibits very low filtered qt values (< 200 kPa) along the section except at site PF05–04, where values are >500 kPa up to 1600 kPa. The seismic horizon (H8, base of Unit 8) is identified at 17 m in PF05–01 and 14 m in PF05–03 on the western side. On the eastern

compartment, H8 is not visible in CPTu data being at depths of over 45 m. From the sub-bottom profile, the horizon is identified at 47, 45 and 40 m (Fig. 8).

Unit 9 (yellow) exhibits notable variations in filtered qt on the western side, with high values reaching 1000 kPa. This trend correlates
with the sub-bottom profile (Fig. 8), where highly reflective seismic horizons and acoustic anomalies are observed. On the western side, the seismic horizon H9 is identified at 34 and 28 m. In the eastern compartment, the seismic horizon is not clearly identified close to the fault, but on the eastern side, it is picked at around 42.5 m depth.

Finally, Unit 10 (grey) is characterized by low filtered qt (< 200 kPa) only visible in PF05–01, located on the western side.

### 4.3. Age model and Sedimentation rate (SR)

Based on core data, seismic horizons H1 to H4 were dated. According to these dated horizons, a mean sedimentation rate (30 ± 5 cm.kyr⁻¹, Fig. 9) was obtained, allowing deeper horizons (from H4 to H8) to be estimated. Isotopic analyses (δ¹⁸O) and radiocarbon dating (¹⁴C) from cores ALB_CL54 and ALB_CL26 (Fig. 9) show good correlation with the isotopic record from IODP Site 977 (Martrat et al., 2004). These correlations provide additional tie-points that refine the age model (Fig. 9) and strengthen the seismostratigraphic framework (Figq. 9 and 10).

The age model spans the last 90 cal. Kyr BP, covering the climatic periods MIS 1 (Holocene), MIS 2, MIS 3, MIS 4 and a part of MIS 5.

The δ¹⁸O values reflect typical glacial and Holocene records, with δ¹⁸O values during MIS 2 (3.70 ‰ for core ALB_CL26 and 3.50 ‰ for ALB_CL54) higher, and lower δ¹⁸O values during the Holocene (0.10 ‰ for ALB_CL26 and 0.09 ‰ for ALB_CL54). The mean sedimentation rate (SR) in cores ALB_CL26 and ALB_CL54 during MIS 1 is up to 120 cm. kyr⁻¹ (~7 cal. Kyr BP). During MIS 2, the ALB_CL54 show a significant increase in SR, reaching up to 150–250 cm.kyr⁻¹ at 15 and 21 kyr, respectively, marking the end of the YD and LGM periods. In contrast, core ALB_CL26 shows a sedimentation rate varying from 10 cm.kyr⁻¹ during the YD period to 75 cm.kyr⁻¹ during the LGM.

The deglaciation period, corresponding to MIS 3 (~30–60 kyr), is visible in core ALB_CL26, with a low sedimentation rate around 10 to 25 cm.kyr⁻¹, while in core ALB_CL54, at 30 kyr, the SR varies from 250 to 150 cm.kyr⁻¹.

The MIS 4 (60–70 kyr) is barely identified in core ALB_CL26, with only few isotopic points, while the warming period of MIS 5 (70–90 kyr) is visible. In this period, the sedimentation rate varies from 25 cm.kyr⁻¹ (~70–72 kyr) to <10 cm.kyr⁻¹ (~72 to 82 kyr), reaching up to 50–100 cm.kyr⁻¹ between 85 and 90 kyr.

### 4.4. Evidence of the northern Bokkoya fault segment activity

The sub-bottom profile PP0130 was chosen because it intersects the segment with the largest vertical displacements of reflectors, which can be associated with normal component movement from the last 120 kyr (Figs. 10 and 11). The main active Bokkoya strike-slip fault displays a cumulative active character, evidenced by strong vertical throws and fan-shaped geometries (Figs. 5 and 8). The profile has been converted to depth and flattened with the seafloor as reference (Figs. 5 and 8A), allowing a more precise quantification of the vertical throw of the Bokkoya fault from each base unit (H8 to H1) (Fig. 10) and the thickness variations of each unit toward the fault. Vertical displacements were measured at the Bokkoya strike-slip fault on the sub-bottom profile using a Vp of 1500 ± 50 m.s⁻¹ (Figs. 5 and 10). The slip rate is estimated using seismic horizon dating (Fig. 10).

Using seismic reflection profiles calibrated in depth with CPTu and cores data, the cumulative vertical fault throws along the Bokkoya fault were determined from oldest (H9, base of Unit 9) to youngest (H1, base of Unit 1) (Figs. 8 and 10). H9 (yellow) did not have its cumulative vertical fault throw estimated due to the resolution in the sub-bottom profile that do not allow the identification of the base of this unit. However, H8 (darker green) has a cumulative offset of 33 ± 1.35 m. H7 (light pink) corresponds to an erosional surface on the western side, with a minimal cumulative vertical fault throw estimated at 25.50 ± 1.10 m. H6 (brown) also corresponds to an erosional surface on the western side of the fault, with a minimum cumulative vertical fault throw was

estimated at 18.75 ± 0.88 m. H5 (purple) has a vertical cumulative throw of 14.25 ± 0.73 m. H4 (green) has a vertical cumulative fault throw of 8.25 ± 0.53 m; H3 (blue) has a vertical cumulative throw estimated at 6.00 ± 0.45 m. H2 (pink, base of Unit 2) and H1 (orange, base of Unit 1) have cumulative vertical fault throws of 3.00 ± 0.35 and 2.25 ± 0.33 m, respectively. Finally, the seafloor has a vertical fault throw estimated at 0.75 ± 0.75 m (Fig. 10).

By plotting the cumulative vertical fault displacement of the Bokkoya fault segment along the sub-bottom profile PP0130 (Fig. 12), two slope variations are observed: from the present to ~45 kyr and from 45 to ~120 kyr. However, at the core scale (depth investigation limit at 40 kyr) from the sub-bottom profile (Figs. 5 and 12C), fewer variations in vertical displacements were calculated. Seven slope variations are identified: from present to 12 kyr, a vertical slip rate of 0.06 mm.kyr⁻¹; from 12 to 17.5kyr, a vertical slip rate of 0.27 mm.kyr⁻¹; from 20 to 21.5 kyr, a vertical slip rate of 1.00 mm.kyr⁻¹; from 21.5 to 40 kyr, a vertical slip rate of 0.08 mm.kyr⁻¹; from 40 to 42 kyr, a vertical slip rate of 0.75 mm.kyr⁻¹. No vertical displacements were found at the core scale, between 17.5 and 20 kyr and 42 to 45 kyr (Fig. 12).

## 5. Discussion

Detailed seismic-stratigraphy and correlation between multiple proxies allow discussion about horizontal and vertical motions along a transect of the northern Bokkoya fault segment and made possible the identification of paleoearthquakes sequences from the last 120 kyr.

The low acoustic penetration of the sub-bottom profiles limits the interpretation of the deep tectonic structures. However, the available high-frequency source enables us to distinguish, with a high vertical resolution, the sediment deposits and fault activity. Although the Bokkoya fault system mainly accommodates sinistral displacements, some of the fault segments exhibit a normal component. Active fault scarps with vertical displacement create local depressions that may contribute to sedimentary deposition (Figs. 5 and 12), which helps decipher paleoearthquake sequences (Fig. 12).

Our findings led to a correlation between multiple proxies, emphasizing the importance of using various tools for maximum accuracy: CPTu data (qt filtered, 0.1 m resolution), sub-bottom sediment imaging (0.25 m vertical resolution) and core data. The integration of data revealed under-sampling and compaction issues during coring operations, as described in Bourillet et al. (2007) for the same calypso corers, or illustrated by Skinner and McCave (2003). Despite the uncertainties associated with coring issues, the correlation between the available geophysical and geotechnical data proxies provides a sufficient precision to calibrate our data set and propose interpretations.

### 5.1. The horizontal motion along the northern Bokkoya fault system

The focal mechanisms, GPS data, and detailed morpho-structural studies indicate that the Al Idrissi fault system is a left-lateral strike-slip fault, with segments exhibiting transtension and transpression (e.g. Stich et al., 2006; Gràcia et al., 2019; Koulali et al., 2011). This system extends southward through the Small Al Idrissi volcano, forming the Bokkoya fault system.

The Al Idrissi fault zone (Al Idrissi and Bokkoya fault systems) appears to accommodate a portion of the regional deformation due to the indentation of the African plate into the Alboran domain (Estrada et al., 2018). According to the literature, the sinistral strike-slip AIFS initiated at Pleistocene, 1.8 Ma and progressively propagates southward, activating the Bokkoya fault system around 0.8–1.1 Ma (Lafosse et al., 2017, Lafosse et al., 2020). This study highlights the volcanic outcrop and relief of the SAIV region, characterized by a horizontal displacement of approximately 3 km along the northern Bokkoya fault system, as identified through bathymetric and seismic reflection data (Figs. 2 and 4). If we consider the initiation of the Bokkoya fault between 1.1 and 0.8 Ma (Lafosse et al., 2020), the offset of the SAIV magmatic basement
<figure><img src="image_9.png" /></figure>

<figure><img src="image_10.png" /></figure>

<figure><img src="image_11.png" /></figure>

(caption on next page)
<figure><img src="image_12.png" /><figcaption>**Fig. 9.** Age model and sedimentation rate of ALB_CL26 and ALB_CL54 cores. The blue curves are isotopic records (δ¹⁸O) and ¹⁴C radiocarbon dating (red stars) from the last 90 ca. kyr BP from cores ALB_CL26 and up to 40 cal. Kyr BP for ALB_CL54 calibrated to IODP 977 (black line, Martrat et al., 2004). The grey bars indicate cold stadials (HS1 to HS8, Heinrich Stadial 1 to 8, and YD Younger Dryas). LGM Last Glacial Maximum, B-A Bølling-Allerød warm period, MIS 1, 2, 3, 4 and 5 correspond to Marine Isotope Stages 1 to 5. The orange lines correspond to the mean sedimentation rate (SR) for each core. See inset for the location of the cores. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>
<table><caption>**Fig. 10.** Table of each horizon (H8 to seafloor) with cumulative vertical fault throws, corrected vertical displacement of each horizons and estimated ages from the main Bokkoya fault of sub-bottom profile PP0130. The ages (kyr) of the different horizons are based of AMS ¹⁴C radiocarbon (¹⁴C) and δ¹⁸O, using a constant sedimentation rate constrained by cores data up to 30 ± 5 cm.kyr⁻¹ (SR) from ALB_CL54. A propagation velocity of 1500 m.s⁻¹ is used to estimate vertical displacements. The uncertainties were calculated with ±50 m.s⁻¹ and the average vertical resolution of 0.25 m from seismic data. Vertical displacement is measured on the Bokkoya strike-slip fault using seismic data (Figs. 5 and 11).</caption><thead><tr><th>Seismic units</th><th>Seismic Horizons</th><th>Age (kyr)</th><th>Cumulative vertical displacement (m)</th><th>Vertical fault throws of each horizon (m)</th><th>Mean vertical slip rate per units (mm.yr<sup>-1</sup>)</th></tr></thead><tbody><tr><td rowspan="3">U1</td><td>Seafloor</td><td>0</td><td>0.75 ± 0.75</td><td>0.75</td><td rowspan="3">0.10</td></tr><tr><td>1</td><td>0.1 (¹⁴C)</td><td>1.50 ± 0.30</td><td>0.75</td></tr><tr><td>2</td><td>3.9 (¹⁴C)</td><td>1.50 ± 0.30</td><td>0.00</td></tr><tr><td rowspan="3">U2</td><td>H1</td><td>14.5 (¹⁴C)</td><td>2.25 ± 0.33</td><td>0.75</td><td rowspan="3">0.13</td></tr><tr><td>4</td><td>17.5 (¹⁴C)</td><td>3.00 ± 0.35</td><td>0.75</td></tr><tr><td>H2</td><td>20 (¹⁴C)</td><td>3.00 ± 0.35</td><td>0.00</td></tr><tr><td rowspan="3">U3</td><td>6</td><td>21.5 (¹⁴C)</td><td>4.50 ± 0.40</td><td>1.50</td><td rowspan="3">0.23</td></tr><tr><td>H3</td><td>33 ± 5 (δ¹⁸O)</td><td>6.00 ± 0.45</td><td>1.50</td></tr><tr><td>7</td><td>40 ± 7 (SR)</td><td>6.75 ± 0.48</td><td>0.75</td></tr><tr><td rowspan="3">U4</td><td>8</td><td>42 ± 7 (SR)</td><td>8.25 ± 0.53</td><td>0.00</td><td rowspan="3">0.18</td></tr><tr><td>H4</td><td>45 ± 7 (SR)</td><td>8.25 ± 0.53</td><td>1.50</td></tr><tr><td>U5</td><td>60 ± 10 (SR)</td><td>14.25 ± 0.73</td><td>6.00</td></tr><tr><td rowspan="3">U6</td><td>H5</td><td>73 ± 12 (SR)</td><td>18.75 ± 0.88</td><td>4.50</td><td rowspan="3">0.34</td></tr><tr><td>H6</td><td>89 ± 15 (SR)</td><td>25.50 ± 1.10</td><td>6.75</td></tr><tr><td>H7</td><td>120 ± 20 (SR)</td><td>33.00 ± 1.35</td><td>7.50</td></tr></tbody></table>

corresponds to a horizontal slip rate ranging from 2.7 to 3.7 mm.yr⁻¹. Revising earlier GPS-based block models (e.g. Vernant et al., 2010), Koulali et al. (2011) estimate a left-lateral strike-slip motion at 3.8 mm. yr⁻¹ with an extensional component at 2 mm.yr⁻¹ along the Al Idrissi fault system, consistent with the calculated moment tensor inversion (Serpelloni et al., 2010; Stich et al., 2006). The magnitude of the estimated horizontal slip rate in our study is consistent with these values derived from current GPS data.

## 5.2. Vertical motion along the northern Bokkoya fault system

The western side of the Al Idrissi fault system is interpreted from the GPS model block as belonging to a rigid block, including the southern Betics, western Alboran Sea, and the central Rif Mountains (Koulali et al., 2011). The current maximum extrusion rates of this block indicate a south westward lateral escape of 5.5 to 6 mm.yr⁻¹ (Koulali et al., 2011; Vernant et al., 2010), which may explain the extensional component recorded on the fault system as well as changes in the orientation of certain segments.

According to the horizontal slip rate deduced from our study (2.7–3.7 mm.yr⁻¹), the fault segment should have undergone a maximum horizontal displacement of 320–450 m over 120 kyr. When examining the blocks on either side of the fault (considering the maximum left-lateral displacement of 500 m, they would have experienced over the past 120 kyr), no significant variation in seismic units' thickness or stratigraphic sequences is observed from the available seismic data base (450 m black scale line, Fig. 3b). This suggests that differences between the two blocks are mainly due to the normal movements, since the last 120kyr.

In the study area, the Small Al Idrissi Volcano acts as a relay, accommodating and distributing the deformation along the Bokkoya and Al Idrissi fault systems. The southern part of the Small Al Idrissi Volcano is associated with the main active sinistral strike-slip Bokkoya Fault, which forms a local subsidence basin elongated along the fault strike (Figs. 2 and 10). Bathymetric data reveal that the subsiding basin is

particularly pronounced near the magmatic basement high. It is 250 m wide, with a maximum elevation of 441 m, and subsidence near the fault is observed over a length of 1.5 km (Figs. 2 and 10). Progressively, a transtensive basin is no longer visible to the south, that be also a result of the relief displacement.

Sub-bottom profile show that the basin is bordered to the west by a major fault, whose motion clearly exhibits a normal fault component (Fig. 5). Analysis of reflector apparent offset suggests that vertical displacement varies significantly along this segment of the Bokkoya fault segment (Fig. 10). The depth difference of each horizon between the eastern and western sides of the fault corresponds to the cumulative vertical coseismic displacements.

Vertical displacement is particularly high at the PP0130 key profile, becoming almost negligible further south (Fig. 11). This suggests that the area just south of the volcano has local transtension. Indeed, the region is affected by significant normal faulting with substantial relative vertical movements between the two sides: the eastern side undergoing subsidence and the western side undergoing uplift (Figs. 5 and 10). These vertical movements decrease southward (from a maximum of 33 to a maximum of 8 cumulative meters, Fig. 10), indicating that the ratio of vertical to horizontal displacement varies significantly along the Bokkoya strike-slip system.

## 5.3. Paleoearthquake sequences and vertical slip rate

This paper focused on one key site based on a very high-resolution sub-bottom profile (Fig. 5) that reveals the recent dynamics of the Bokkoya sinistral fault, characterized by a normal component that shifts the sedimentary series. In the fault zone, significant variations in sedimentation rates are recorded (Figs. 8 and 9B), with higher rates within the fault zone (up to 180–250 cm.kyr⁻¹ around 15, 17.5,21 and 30 kyr) and lower rates farther from the fault zone on the western and eastern fault blocks (up to 50 cm.kyr⁻¹ at the same period). This suggests that the depression zone does not correspond to a moat system controlled by deep-water currents, where lower sedimentation rates would be
<figure><img src="image_13.png" /><figcaption>**Fig. 11.** Left: Bathymetric map of the Small Al Idrissi Volcano (SAIV) showing morphology (drifts, moats), structural features (relay zone) and topographic high with the position of two sub-bottom profiles (PP0130, PP0240) visible in Fig. 5. Right: The graph shows the cumulative vertical displacement along the main Bokkoya fault over the last 120 kyr. Comparing with the PP0240 sub-bottom profile further to the south, the cumulative vertical displacement is less significant, with a strike-slip component.</figcaption></figure>

expected (Figs. 5 and 8). The sedimentary deposits in the subsiding basin are driven by tectonic processes with a downthrown component and could be characterized as a fault-controlled drift (Reesco et al., 2014; Liu et al., 2021) (Fig. 5).

The presence of an active fault with vertical slip creates variations in sediment thickness on either side of the fault, resulting in fan-shaped geometries identified as syn-tectonic deposits (in yellow, Fig. 12A and Fig. 5). Shifts in sedimentary series along the main fault scarp provide evidence of co-seismic events (Figs. 5 and 12A and D). Barnes and Pondard (2010) explain that the presence of a permanent fault scarp facilitates continuous sedimentation, identified as a post-seismic growth sequence (PS, in yellow, Fig. 12C and D). They also note that the displacement history curve approaches a linear relationship but never flattens (Fig. 12D). Our quantified vertical fault throws, derived from high-resolution seismic data analysis, reveal the presence of a persistent fault scarp since 120 kyr (Fig. 12D). A slight inflection around horizon H7 is observed at ~94 kyr with a vertical slip rate variation of 0.30 mm. yr⁻¹ compared to 0.27 mm.yr⁻¹ from 120 to 94 kyr (Fig. 12D). This inflection could suggest a cumulative paleoearthquake episode, named EQc4. However, EQc4 may be a time of fault increasing activity and the change rate as evidence of the occurrence of an earthquake seems not well preserved as EQc1, EQc2 or EQc3. Over the last 45 kyr, the mean vertical slip rate is calculated to be up to 0.17 mm.yr⁻¹.

The resolution of our data, with episode of intense erosion, does not allow us to clearly distinguish paleoearthquakes. In the western fault block (Figs. 5 and 8), horizons H5, H6, and H7 are identified as erosional surfaces based on both the available sub-bottom profiles, the CPTu data and the ALB_CL26 core (Figs. 8, 11B, and C). The absence of deposition or the erosion of Units 7 and 6 in the western drift of the main Bokkoya fault can be attributed to both tectonic activity and bottom-current dynamics during the period spanning approximately 94 to 73 kyr. A numerical modelling study (Maniatis et al., 2009) suggests that erosion and sediment deposition could affect the behaviour of normal faults by accelerating their slip rate. In our study, the vertical fault throws measured (Fig. 10) represent minimum values influenced by erosion, which limits the accurate identification of paleoearthquake events. The western fault block does not preserve the post-seismic and inter-seismic sequences well.

However, at the scale of the sub-bottom profile, the data show a clear change in the vertical slip rate for this segment. Fig. 12 shows a decrease in the slip rate from 45 ky (H4 horizon, unit base of U4). The slip rate was, on average, higher (0.30 mm.yr⁻¹) between 94 and 42 kyr and lower from 42 kyr to the present day (mean of 0.17 mm.yr⁻¹) (Fig. 12D).

Between 94 and 45 kyr, four horizons, H8, H7, H6, and H5, show minimal vertical cumulative displacements of 33 m, 25.50 m, 18.75 m, and 14.25 m, respectively (non-cumulative throws range from 7.50 to 6 m, Fig. 10).

At the scale of the sub-bottom profile (~120 ky) (Fig. 12D), we observe a slowdown in fault activity since 45 kyr, which could be related to the migration of deformation along the fault system or an increase in the horizontal component of the fault relative to the vertical component.

Over the past 30 years, four moderate earthquakes (with magnitudes between 6.0 and 6.4 Mw) have occurred near the Bokkoya fault system (Fig. 1B). In 1994, a Mw 6.0 earthquake (Calvert et al., 1997; El Alami et al., 1998) was associated with the Bousekkour-Aghbal onshore-offshore normal-left-lateral fault (d'Acremont et al., 2014). In 2004, a Mw 6.3 earthquake struck near Al Hoceima; while the exact source remains debated, it is considered to be onshore (Ait Brahim et al., 2004; Tahayt et al., 2009). Recently, Lozano et al. (2025) specified that the inland series is aligned to the west of the Trougout fault. In 2016 and 2021, Mw 6.4 and Mw 5.3 earthquakes, respectively, were relied to the central Al Idrissi fault system, north of the Small Al Idrissi Volcano (Lozano et al., 2025; Gràcia et al., 2019; Kariche et al., 2018; Medina and Cherkaoui, 2017). On a short scale time, seismicity appears to migrate along the Al Idrissi fault system. A recent study by Lozano et al., 2025 relocated hypocenters of the 2021 and 2016 series at the eastern and western boundary of the Al Idrissi fault system, respectively. It has been suggested that the 2016 series shows great accuracy with the AIFS, and the eastern 2021 series could be related to the unmapped structure of the AIFS (Lozano et al., 2025, Fig. 1B and C). In fact, the predominance of low to moderate events with magnitude (Mw < 3) and shallow seismicity with a swarm-type sequence (Fig. 1C) could indicate a readjustment of the stress release with low to moderate events in the area, rather than larger mainshock like the 2004 or 2016 events (Lozano et al., 2025).

In our analysis, we assume that there is no long-term interseismic creep, so all recorded vertical displacements are the sum of coseismic displacements. However, although the studied segment of the Bokkoya fault has not experienced significant historical seismicity, it does exhibit seismic activity with magnitudes lower than 3 (Fig. 1C). This low seismicity currently recorded along the Bokkoya fault segment, along with the low and continuous vertical slip rate observed in our study, could be associated with creeping. Several studies have shown that active faults can exhibit creeping with aseismic behaviour during slow but continuous deformation, as seen in the Sea of Marmara, where low-magnitude events (Mw ~ 2-3) are recorded (Bohnhoff et al., 2017; Gasperini et al.,
<figure><img src="image_14.png" /><figcaption>**Fig. 12.** Coseismic evidence from the main Bokkoya fault segment. (A) Zoom on the main Bokkoya strike-slip fault with a normal component with seafloor flattened (Profile PP0130, Fig. 2 for location). Syn-tectonic deposits inside units, especially in U4, characterized by fan-shaped geometries are observed (in yellow). In yellow, post-seismic growth sequences (PS) show the thickening near the main fault. (B) The isotopic analysis and sedimentation rate from ALB_CL54 identified variations near the main Bokkoya fault. (C) Vertical fault throw was determined more precisely with radiocarbon age from core ALB_CL54. The variation of vertical slip rate varies from 0.06 mm.yr⁻¹ up to 1.00 mm.yr⁻¹, and at least three variations of the vertical slip rate are identified, and three possible paleoearthquakes events (EQc) from the last 45 kyr.(D) Vertical fault throws and the mean vertical slip rate from the last 120 kyr was determined from the PP0130 sub-bottom profile, and at least three variations in the average fault activity is observed varying from 0.17 mm.yr⁻¹ to 0.30 mm.yr⁻¹. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

2018).

Creeping could be associated with a context of tensile step-over, as explained by models predicting significant off-fault plasticity (Mia et al., 2024). This plastic deformation results in irregular strain distribution within the overlapping region due to partial ruptures transfer across the step-over. These findings may align with observations at the transition between the Bokkoya and Al Idrissi fault systems, that the young and narrow stepover might only permit small-width rupture jumps (Duan and Oglesby, 2006).

By examining variations in vertical fault throw and sedimentation rates at the core scale (over the last 45 kyr; ALB_CL54, Figs. 11B and C), we can link changes in vertical slip velocity to paleoearthquake events. Over the last 45 kyr, at least three cumulative paleoearthquake episodes (EQc1 to EQc3) and associated post-seismic growth sequences (PS1 to PS3) are identified (Fig. 12C):

From ~45 kyr (horizon H4) to 42 kyr, the vertical fault throw value is zero, interpreted as an inter-seismic episode (Figs. 10 and11C). From 42 to 40 kyr (PS3), a vertical slip rate of 0.75 mm.yr⁻¹ is linked to post-seismic growth sequences and the EQc3 episode (Fig. 12C). A higher sedimentation rate is recorded from this period around 30–32 kyr, reaching up to 225 cm.yr⁻¹, which corroborates the cumulative earthquake crises in this fault zone.

From 40 to 21.5 kyr, a change in vertical slip rate is identified at horizon 8 (0.08 mm.yr⁻¹), showing a deceleration of the fault activity (Fig. 12C). This suggests a change in the fault dynamic that could be linked to an interseismic episode or creeping events. By comparing sedimentation rates from core ALB_CL26 and ALB_CL54 (Fig. 9), the sedimentation rate is slightly higher in the fault zone (> 50 to 225 cm. kyr⁻¹) than in the western block (~30/25 cm.kyr⁻¹).

From 21.5 to 20 kyr (PS2): a fan-shaped geometry is observed
between limit 6 and H2 horizons, covered and preserved by a uniformly thick sequence (horizon H2–4 limit, 20 to 17.5 ka) (Fig. 12A). A minimal vertical slip rate of 1.00 mm.yr⁻¹ (from sub-bottom profiles) and sedimentation rates over 250 cm.yr⁻¹ (core ALB_CL54) correlate with an EQc2 episode (Figs. 12B and C). Moreover, during the Last Glacial Maximum (LGM), the mean sedimentation rate in IODP 977 is around 50 cm.yr⁻¹, and lower in the ALB_CL26 from the western drift (~ 25 to 40 cm.kyr⁻¹), meaning that faulting created accommodation space in the subsiding basin, facilitating sediment deposition.

From 17.5 to 12 kyr (PS1), a fan-shaped geometry is observed between boundaries 4 and 2, centred on the H1 horizon in the sub-bottom profile (Figs. 12A and C), indicating syn-tectonic deposits. A vertical slip rate of 0.27 mm.yr⁻¹ and a higher sedimentation rate are calculated for this period from vertical displacement throws and isotopic analysis (Fig. 11B). A peak in sedimentation of up to 180 cm.yr⁻¹ is associated with an earthquake crisis episode (EQc1). A well-preserved post-seismic growth is covered by a uniformly thick sequence on both sides of the main Bokkoya fault. To support the presence and preservation of an earthquake crisis episode, observations from core ALB_CL26, located on the western block of the main Bokkoya fault (Fig. 5), indicate a relatively low sedimentation rate of <20 cm.yr⁻¹ (Fig. 9B). In contrast, core ALB_CL54, located in the subsided basin near the main Bokkoya fault, shows a sedimentation rate close to 250 cm.yr⁻¹ (Fig. 9A). An average sedimentation rate of around 125 cm.yr⁻¹ during the same timeframe was found in the reference core IODP 977, which is far from the site and unaffected by tectonic processes (Fig. 9C). Relatively high sedimentation rates in Alboran are described in the literature, linked to the interglacial/glacial transition. Intensified Mediterranean bottom currents at the onset of the Younger Dryas / Heinrich Stadials 1 have been proposed by several authors (Moreno et al., 2002; Frigola et al., 2012; Trias-Navarro et al., 2023).

Before 12kyr, a lower mean vertical displacement (0.12 mm.yr⁻¹, Fig. 12C) suggests a phase of relative slowdown in fault movement, potentially related to low magnitude coseismic events or creeping processes or predominantly strike-slip motion. The present-day fault scarp of 0.75 m on the seafloor indicates recent fault activity.

In summary, four majors earthquakes episodes (EQc1 to EQc4) are potentially preserved along this strike-slip fault segment in the local transtensional basin. At the core scale (last 45 kyr), at least three main events (15/17.5 kyr, 21.5 kyr, and 42 kyr) show a pulse of vertical fault throw and locally higher sedimentation rates in the fault zone, suggesting localized deformation along this segment with a normal faulting component. Low or absent vertical slip rates may also indicate strike-slip displacement rather than fault inactivity.

The deformation rate was higher between 120 and 45 kyr, reaching up to 0.30 mm.yr⁻¹, compared to the period from 45 kyr to the present, where the rate slowed down to a mean of 0.17 mm.yr⁻¹ along the main Bokkoya fault segment. However, over the last 45 kyr, at least three preserved events with pulses of vertical fault throw up to 0.27, 1.00 and 0.75 mm.yr⁻¹ were identified.

Along the Al Idrissi fault system, previous studies have shown variability in the vertical displacement rate, with orders of magnitude similar to our study. Estrada et al., 2021 found an average vertical slip rate of 0.1 mm.yr⁻¹ since 4.57 Ma for the Averroes Fault, which also exhibits local transtension (Fig. 1). Bell et al., 1997 identified a small slip rate (~0.05–0.1 mm.yr⁻¹) over the last 100 kyr in the Carboneras Fault (Fig. 1A). Tendero-Salmerón et al., 2021 calculated vertical throw rates of up to 0.47 mm.yr⁻¹ since 280 kyr on the southern Bokkoya fault system. The authors show that, during the last 25 kyr, a clear acceleration in fault dynamic occurred, and deformation localized on the southern Bokkoya fault system.

The moment magnitude (Mw) can be estimated based on the vertical displacement and the fault rupture length (Hanks and Kanamori, 1979; Wells and Coppersmith, 1994). Considering a segment length of 5 km (between the Small Al Idrissi Volcano and the relay zone, Fig. 11) and a vertical displacement of 1.5 m (EQc1, EQc2 and EQc3), the minimum

estimated moment magnitude would be Mw 6.1. Actually, significant erosion and horizontal motion limit our ability to estimate the moment magnitudes precisely. We focused on and quantified the vertical displacement using the method of Barnes and Pondard (2010), which leads to an underestimation of the magnitude, as it does not account for the erosion that removes information, the presence of the permanent fault scarp, or unquantified horizontal strike-slip motion.

A similar study by Estrada et al., 2021 shows comparable results for the estimated moment magnitude. Their study modelled the tsunamic potential of the vertical seafloor offsets to the Averroes strike-slip fault (Fig. 1A). A rapid co-seismic displacement of the seafloor, with a length of 22 km and net slip of 5.4 m could generate an earthquake with a magnitude of Mw 7. Their study also demonstrates that tsunami propagation is influenced by seafloor deformation, reaching Moroccan and Spanish coasts.

If we consider a stepover configuration with two parallel faults having a gap at the scale of the SAIV magmatic body, the geometric complexity in depth can play an important role in generating significantly different seismicity patterns and probability of rupture propagation (Mia et al., 2024).

This highlights the need to improve paleoearthquake models to better estimate risks (both tsunamigenic and seismogenic), particularly in relation to strike-slip faults and local transtension. Numerous onshore and offshore faults, such as the San Andreas Fault (Goldfinger et al., 2007), the Marmara Sea (Gasperini et al., 2018), and the strike-slip Wairau Fault, considered as a major seismic hazard in central New Zealand, partially submarine (Barnes and Pondard, 2010). In the westernmost Mediterranean Sea, strike-slip faults with vertical offsets have the potential to cause destructive tsunamis (Estrada et al., 2021). In the last 200 years, several earthquakes ranging from Mw 5.9 to 6.4 have occurred in the Alboran Sea region, northern Morocco (Gràcia et al., 2019), and the AIFS may be capable of generating larger events.

## 6. Conclusion

This study highlights the complexity of recognizing paleo-earthquakes along the sinistral strike-slip Al Idrissi fault and its relay with the Bokkoya fault are emphasized. By employing a multi-proxy approach that combines sub-bottom profiles, bathymetric data, CPTu, and core samples, we are able to establish precise correlations and dating between these various indicators. This comprehensive approach enhances the understanding of paleoseismic events in the Small Al Idrissi Volcano region, located south of the Alboran Sea. The results demonstrate that the northern Bokkoya fault, a strike-slip fault, is influenced by vertical displacements within a transtensive basin. However, the presence of a permanent fault scarp complicates the preservation of paleoearthquakes records in sedimentary sequences. Despite this challenge, at least four cumulative paleoearthquake events over the last 120 kyr have been recorded. Furthermore, the study shows a global deceleration in Bokkoya fault activity (in terms of vertical motion) over the past 45 kyr, with an average vertical slip rate of 0.17 mm.yr⁻¹, compared to 0.30 mm.yr⁻¹ between 45 and 94 kyr and 0.27 mm.yr⁻¹ from 94 to 120 kyr. Detailed core analysis and sub-bottom profile interpretations along the main fault reveal significant fluctuations in fault activity. These include the presence of syn-tectonic deposits and notable increases in sedimentation rates near the fault. At least three recent preserved cumulative paleoearthquake episodes, dated to 17.5, 21.5, and 42 kyr, have been identified. This study emphasizes the value of a multi-proxy approach for accurately assessing variations in fault activity and highlights the challenges of interpreting geophysical and sedimentary signals within the context of a transtensive basin. These findings lay the groundwork for future research on the evolution of tectonic activity in the region and its interactions with climatic and oceanographic events.
CRediT authorship contribution statement

**L. Vidil:** Writing – review & editing, Writing – original draft, Methodology, Data curation, Investigation, Visualization. **E. d'Acremont:** Writing – review & editing, Validation, Supervision, Methodology, Funding acquisition, Conceptualization, Data curation, Project administration, Resources, Investigation. **L. Emmanuel:** Writing – review & editing, Supervision, Methodology, Investigation. **F. Caroir:** Writing – review & editing. **S. Lafuerza:** Writing – review & editing, Methodology, Conceptualization, Data curation, Investigation, Funding acquisition. **S. Leroy:** Writing – review & editing, Validation, Conceptualization, Investigation. **G. Ercilla:** Writing – review & editing, Validation, Conceptualization. **A. Rabaute:** Visualization, Data curation, Investigation. **J. Galindo-Zaldivar:** Writing – review & editing, Validation. **E.M. Latni:** Visualization, Data curation, Investigation. **A. Guittet:** Visualization, Methodology. **J.F. Brouillet:** Visualization, Data curation, Conceptualization.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The ALBACORE cruise was mainly funded by the French Oceano-
graphic Fleet (FOF). We thank Captain G. Bourret of R/V Pourquoi Pas?
and its crews and technicians, and GENAVIR team for the data
collection.

This post-cruise research is funded in whole or in part by the French National Research Agency (ANR) in the framework of the ALBANEO project "ANR-22-EDIR-0001-01 and ANR-22-EDIR-0001-02". Gemma Ercilla and Jesús Galindo-Zaldivar acknowledge the support of the project PID2022-136678NB-I00 AEI/FEDER financed by MICIU/AEI 10 .13039/5011000011033 and FEDER, UE. We thank the AWI for the MSCL bench, Catalina Gebhardt from Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research. We thank Lou TORCQ, Virginia ROJAS for their participation to the isotopic and radiocarbon analysis on sediment cores. The processed seismic data were interpreted using Kingdom IHS Suite© software. Finally, we also thank Pr Éric Verrecchia from IDYST Institute, Lausanne University (Switzerland), for his help in mathematical issues, that allow us to obtain a filtered cone resistance (qt_filtered) from in-situ penetrometer CPTu data. The Editor and re-views by Jacques Déverchère and anonymous reviewer are gratefully acknowledged.

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.
org/10.1016/j.tecto.2025.230922.

Data availability

Data will be made available on request.

References

Ait Brahim, L., Nakhcha, C., Tadili, B., et al., 2004. Structural analysis and interpretation of the surface deformations of the February 24th, 2004 Al Hoceima earthquake. Centre Sismologique Euro-Mediterranéen European-Mediterranean Seismological Centre www.emsc-csem.org, 110, no 10.

Amorosi, A., Marchi, N., 1999. High-resolution sequence stratigraphy from piezocone tests: an example from the late Quaternary deposits of the southeastern Po Plain. Sediment. Geol. 128, 67–81. https://doi.org/10.1016/S0037-0738(99)00062-7.

Badhani, S., Cattaneo, A., Collico, S., Urgeles, R., Dennielou, B., Leroux, E., Colin, F.,
Garziglia, S., Rabineau, M., Droz, L., 2020. Integrated geophysical, sedimentological

and geotechnical investigation of submarine landslides in the Gulf of Lions (Western Mediterranean) SP 500, 359–376. https://doi.org/10.1144/SP500-2019-175.

Barnes, P.M., Nicol, A., 2004. Formation of an active thrust triangle zone associated with structural inversion in a subduction setting, eastern New Zealand. Tectonics 23, 2002TC001449. https://doi.org/10.1029/2002TC001449.

Barnes, P.M., Pondard, N., 2010. Derivation of direct on-fault submarine paleoearthquake records from high-resolution seismic reflection profiles: Wairau Fault, New Zealand. Geochem. Geophys. Geosyst. 11. https://doi.org/10.1029/2010GC003254, 2010GC003254.

Beck, C., Mercier De Lépinay, B., Schneider, J.-L., Cremer, M., Çağatay, N., Wendenbaum, E., Boutareaud, S., Ménot, G., Schmidt, S., Weber, O., Eris, K., Armijo, R., Meyer, B., Pondard, N., Gutscher, M.-A., Turon, J.-L., Labeyrie, L., Cortijo, E., Gallet, Y., Bouquerel, H., Gorur, N., Gervais, A., Castera, M.-H., Londeix, L., De Rességuéier, A., Jaouen, A., 2007. Late Quaternary co-seismic sedimentation in the Sea of Marmara's deep basins. Sediment. Geol. 199, 65–89.
https://doi.org/10.1016/j.sedgeo.2005.12.031.

Bell, J.W., Amelung, F., King, G.C.P., 1997. Preliminary late quaternary slip history of the Carboneras fault, Southeastern Spain. J. Geodyn. 24, 51–66. https://doi.org/10.1016/S0264-3707(96)00029-4.

Biggs, J., Bergman, E., Emmerson, B., Funning, G.J., Jackson, J., Parsons, B., Wright, T.J., 2006. Fault identification for buried strike-slip earthquakes using InSAR: the 1994 and 2004 Al Hoceima, Morocco earthquakes. Geophys. J. Int. 166, 1347–1362.
https://doi.org/10.1111/j.1365-246X.2006.03071.x

Billi, A., Cuffaro, M., Orecchio, B., Palano, M., Presti, D., Totaro, C., 2023. Retracing the Africa–Eurasia nacent convergent boundary in the western Mediterranean based on earthquake and GNSS data. Earth Planet. Sci. Lett. 601, 117906. https://doi.org/10.1016/j.epsl.2022.117906.

Bohnhoff, M., Wollin, C., Domigall, D., Küperkoch, L., Martínez-Garzón, P., Kwiatek, G., Dresen, G., Malin, P.E., 2017. Repeating Marmara Sea earthquakes: indication for fault creep. Geophys. J. Int. 210, 332–339. https://doi.org/10.1093/gji/ggx169.

Bouhali, K., Rouai, M., Dekayir, A., Essaied, A., 2025. The south ALBORAN basin seismic swarm in 2020-2021 and its possible relation to the southern development of the al- IDRISSI fault system. Geodin. tektonofiz. 16, 0804. https://doi.org/10.5800/GT- 2025-16-1-0804.

Bourillet, J.-F., Damy, G., Dussud, L., Sultan, N., Woerther, P., Migeon, S., 2007. Behaviour of a Piston Corer from Accelerometers and New Insights on Quality of the Recovery.

Buforn, E., Pro, C., Sanz De Galdeano, C., Cantavella, J.V., Cesca, S., Caldeira, B., Udías, A., Mattesini, M., 2017. The 2016 south Alboran earthquake (Mw = 6.4): a reactivation of the Ibero-Maghrebian region? Tectonophysics 712–713, 704–715.
https://doi.org/10.1016/j.tecto.2017.06.033.

Bull, J.M., Barnes, P.M., Lamarche, G., Sanderson, D.J., Cowie, P.A., Taylor, S.K., Dix, J. K., 2006. High-resolution record of displacement accumulation on an active normal fault: implications for models of slip accumulation during repeated earthquakes. J. Struct. Geol. 28, 1146–1166. https://doi.org/10.1016/j.jsg.2006.03.006.

Burbank, Douglas W., Anderson, Robert S., 2001. Geomorphic Markers. Burbank, DW & Anderson, RS, Tectonic Geomorphology. Malden:(ed.). Blackwell Publishing, pp. 13–32.

Calais, E., Camelbeeck, T., Stein, S., Liu, M., Craig, T.J., 2016. A new paradigm for large earthquake in stable continental plate interiors. Geophys. Res. Lett. 43. https://doi.org/10.1002/2016GL070815.

Calvert, A., Gomez, F., Seber, D., Barazangi, M., Jabour, N., Ibenbrahim, A., Demnati, A., 1997. An integrated geophysical investigation of recent seismicity in the Al-Hoceima region of North Morocco. Bull. Seismol. Soc. Am. 87, 637–651. https://doi.org/10.1785/BSSA0870030637.

Coplen, T.B., 1996. New guidelines for reporting stable hydrogen, carbon, and oxygen isotope-ratio data. Geochim. Cosmochim. Acta 60, 3359–3360. https://doi.org/10.1016/0016-7037(96)00263-3.

Crespo-Blanc, A., De Lamotte, D.F., 2006. Structural evolution of the external zones derived from the Flysch trough and the South Iberian and Maghrebian paleomargins around the Gibraltar arc: a comparative study. Bulletin de la Société Géologique de France 177, 267–282. https://doi.org/10.2113/gssgbull177.5.267.

Crone, A.J., Machette, M.N., Bowman, J.R., 1997. Episodic nature of earthquake activity in stable continental regions revealed by palaeoseismic studies of Australian and north American quaternary faults. Aust. J. Earth Sci. 44, 203–214. https://doi.org/10.1080/08120099708728304.

d'Acremont, E., Lafuerza, S., 2021. ALBACORE Cruise. https://doi.org/10.17600/18001351.

d'Acremont, E., Gutscher, M.-A., Rabaute, A., Mercier de Lépinay, B., Lafosse, M., Poort, J., Ammar, A., Tahayt, A., Le Roy, P., Smit, J., Do Couto, D., Cancouët, R., Prunier, C., Ercilla, G., Gorini, C., 2014. High-resolution imagery of active faulting offshore Al Hoceima, Northern Morocco. Tectonophysics 632, 160–166. https://doi.org/10.1016/j.tecto.2014.06.008.

d'Acremont, E., Lafosse, M., Rabaute, A., Teurquety, G., Do Couto, D., Ercilla, G., Juan, C., Lépinay, B.M., Lafuerza, S., Galindo-Zaldivar, J., Estrada, F., Vazquez, J.T., Leroy, S., Poort, J., Ammar, A., Gorini, C., 2020. Polyphase Tectonic Evolution of Fore-Arc Basin Related to STEP Fault as Revealed by Seismic Reflection Data from the Alboran Sea (W-Mediterranean). Tectonics 39. https://doi.org/10.1029/2019TC005885.

d'Acremont, E., Lafuerza, S., Rabaute, A., Lafosse, M., Jollivet Castelot, M., Gorini, C., Alonso, B., Ercilla, G., Vazquez, J.T., Vandorpe, T., Juan, C., Migeon, S., Ceramicola, S., Lopez-Gonzalez, N., Rodriguez, M., El Moumni, B., Benmarha, O., Ammar, A., 2022. Distribution and origin of submarine landslides in the active margin of the southern Alboran Sea (Western Mediterranean Sea). Mar. Geol. 445, 106739. https://doi.org/10.1016/j.margeo.2022.106739.
De Larouzière, F.D., Bolze, J., Bordet, P., Hernández, J., Montenat, C., Ott d'Estevou, P., 1988. The Betic segment of the lithospheric Trans-Alboran shear zone during the late Miocene. Tectonophysics 152, 41–52. https://doi.org/10.1016/0040-1951(88) 90028-5.

DeMets, C., Iaffaldano, G., Merkouriev, S., 2015. High-resolution fault geomechanics and Quaternary estimates of Nubia-Eurasia-North America Plate motion. Geophys. J. Int. 203, 416–427. https://doi.org/10.1016/j.gjiy.ggy277.

Duan, B., Oglesby, D.D., 2006. Heterogeneous fault stresses from previous earthquakes and the effect on dynamics of parallel strike-slip faults. J. Geophys. Res. 111. https:// doi.org/10.1029/2005JB004138, 2005JB004138.

El Alami, S.O., Tadili, B.A., Chernaoui, T.E., Medina, F., Ramdani, M., Brahim, L.A., Harnafi, M., 1998. The Al Hoceima earthquake of May 26, 1994 and its aftershocks: a seismotectonic study. Ann. Geophys. 41, 4. https://doi.org/10.4401/ag.3801.

Ercilla, G., Juan, C., Hernández-Molina, F.J., Bruno, M., Estrada, F., Alonso, B., Casas, D., Farran, Marcel. If, Llave, E., García, M., Vázquez, J.T., D'Acremont, E., Gorini, C., Palomino, D., Valencia, J., El Moumni, B., Ammar, A., 2016. Significance of bottom currents in deep-sea morphodynamics: an example from the Alboran Sea. Mar. Geol. 378, 157–170. https://doi.org/10.1016/j.margeo.2015.09.007.

Ercilla, G., Juan, C., Periáñez, R., Alonso, B., Abril, J.M., Estrada, F., Casas, D., Vázquez, J.T., d'Acremont, E., Gorini, C., El Moumni, B., Do Couto, D., Valencia, J., 2019. Influence of alongslope processes on modern turbidite systems and canyons in the Alboran Sea (southern Mediterranean). Deep-Sea Res. I Oceanogr. Res. Pap. 144, 1–16. https://doi.org/10.1016/j.dsr.2018.12.002.

Ercilla, G., Vázquez, J.-T., Alonso, B., Bárcenas, P., Casas, D., d'Acremont, E., Estrada, F., Hernández-Salas, L.M., Galindo-Zaldívar, J., Juan, C., Lobo, F., López-González, N., Palomino, D., Sánchez-Guillamón, O., Chourak, M., Gil, A., Gómez-Ballesteros, M., El Moumni, B., Peláez, J.A., Valencia, J., Gorini, C., 2021. Seafloor Morphology and Processes in the Alboran Sea. In: Báez, J.C., Vázquez, J.-T., Caminas, J.A., Malouli Idrissi, M. (Eds.), Alboran Sea - Ecosystems and Marine Resources. Springer International Publishing, Cham, pp. 157–205. https://doi.org/10.1007/978-3-030- 65516-7-6.

Estrada, F., Galindo-Zaldívar, J., Vázquez, J.T., Ercilla, G., d'Acremont, E., Alonso, B., Gorini, C., 2018. Tectonic indentation in the central Alboran Sea (westernmost Mediterranean). Terra Nova 30, 24–33. https://doi.org/10.1111/ter.12304.

Estrada, F., González-Vida, J.M., Peláez, J.A., Galindo-Zaldívar, J., Ortega, S., Macías, J., Vázquez, J.T., Ercilla, G., 2021. Tsunami generation potential of a strike-slip fault tip in the westernmost Mediterranean. Sci. Rep. 11, 16253. https://doi.org/10.1038/ s41598-021-95729-6.

Frigola, J., Canals, M., Cacho, I., Moreno, A., Sierro, F.J., Flores, J.A., Berné, S., Jouet, R., Dennielou, B., Herrera, G., Pasqual, C., Grimalt, J.O., Galavazi, M., Schneider, R., 2012. A 500 kyr record of global sea-level oscillations in the Gulf of Lion, Mediterranean Sea: new insights into MIS 3 sea-level variability. Clim. Past 8, 1067–1077. https://doi.org/10.5194/cp-8-1067-2012.

Galindo-Zaldívar, J., Ercilla, G., Estrada, F., Catalán, M., d'Acremont, E., Azzouz, O., Casas, D., Chourak, M., Vazquez, J.T., Chalouan, A., Sanz de Galdeano, C., Benmakhlouf, M., Gorini, C., Alonso, B., Palomino, D., Rengel, J.A., Gil, A.J., 2018. Imaging the growth of recent Faults: the Case of 2016-2017 Seismic Sequence Sea Bottom Deformation in the Alboran Sea (Western Mediterranean). Tectonics 37, 2513–2530. https://doi.org/10.1029/2017TC00491.

Gasperini, L., Polonia, A., Çagatay, M.N., 2018. Fluid flow, deformation rates and the submarine record of major earthquakes in the Sea of Marmara, along the North- Anatolian Fault system. Deep-Sea Res. II: Top. Stud. Oceanogr. 153, 4–16. https:// doi.org/10.1016/j.dsr2.2018.03.004.

Geist, E.L., Lynett, P.J., 2014. Source Processes for the Probabilistic Assessment of Tsunami Hazards. Oceanography 27 (2), 86–93. JSTOR. http://www.jstor.org/ stable/24862158.

Goldfinger, C., Morey, A.E., Nelson, C.H., Gutiérrez-Pastor, J., Johnson, J.E., Karabanov, E., Chaytor, J., Eriksson, A., 2007. Rupture lengths and temporal history of significant earthquakes on the offshore and north coast segments of the Northern San Andreas Fault based on turbidite stratigraphy. Earth Planet. Sci. Lett. 254, 9–27. https://doi.org/10.1016/j.epsl.2006.11.017.

Gómez De La Peña, L., Gràcia, E., Maesano, F.E., Basili, R., Kopp, H., Sánchez-Serra, C., Scala, A., Romano, F., Volpe, M., Piatanesi, A., Ranero, C.R., 2022. A first appraisal of the seismogenic and tsunamigenic potential of the largest fault systems in the westernmost Mediterranean. Mar. Geol. 445, 106749. https://doi.org/10.1016/j. margeo.2022.106749.

Gràcia, E., Grevesmeyer, I., Bartolomé, R., Perea, H., Martínez-Loriente, S., Gómez de la Peña, L., Villasenor, A., Klinger, Y., Lo Iacono, C., Diez, S., Calahorrano, A., Camafort, M., Costa, S., d'Acremont, E., Rabaute, A., Ranero, C.R., 2019. Earthquake crisis unveils the growth of an incipient continental fault system. Nat. Commun. 10, 3482. https://doi.org/10.1038/s41467-019-11064-5.

Hanks, T.C., Kanamori, H., 1979. A moment magnitude scale. J. Geophys. Res. 84, 2348–2350. https://doi.org/10.1029/JB084Ib05p02348.

Heaton, T.J., Köhler, P., Butzin, M., Bard, E., Reimer, R.W., Austin, W.E.N., Bronk Ramsey, C., Grootes, P.M., Hughen, K.A., Kromer, C., Reimer, P.J., Adkins, J., Burke, A., Cook, M.S., Olsen, J., Skinner, L.C., 2020. Marine20—the marine radiocarbon age calibration curve (0–55,000 cal BP). Radiocarbon 62, 779–820. https://doi.org/10.1017/RDC.2020.68.

Henares, J., Hamdache, M., Peláez, J.A., Sanz De Galdeano, C., López Casado, C., 2024. Multifractal temporal analysis of seismicity of the Trans-Alboran shear zone. Phys. Chem. Earth Part A/B/C 134, 103557. https://doi.org/10.1016/j.pce.2024.103557.

Juan, C., Ercilla, G., Javier Hernández-Molina, F., Estrada, F., Alonso, B., Casas, D., García, M., Farran, M., Llave, E., Palomino, D., Vázquez, J.-T., Medialdea, T., Gorini, C., d'Acremont, E., El Moumni, B., Ammar, A., 2016. Seismic evidence of current-controlled sedimentation in the Alboran Sea during the Pliocene and

Quaternary: Palaeoceanographic implications. Mar. Geol. 378, 292–311. https://doi. org/10.1016/j.margeo.2016.01.006.

Juan, C., Ercilla, G., Estrada, F., Alonso, B., Casas, D., Vázquez, J.T., d'Acremont, E., Medialdea, T., Hernández-Molina, F.J., Gorini, C., El Moumni, B., Valencia, J., 2020. Multiple factors controlling the deep marine sedimentation of the Alboran Sea (SW Mediterranean) after the Zanclean Atlantic Mega-flood. Mar. Geol. 423, 106138. https://doi.org/10.1016/j.margeo.2020.106138.

Kariche, J., Meghraoui, M., Timoulali, Y., Cetin, E., Toussaint, R., 2018. The Al Hoceima earthquake sequence of 1994, 2004 and 2016: stress transfer and poroelasticity in the Rif and Alboran Sea region. Geophys. J. Int. 212, 42–53. https://doi.org/ 10.1093/gji/ggx385.

Koulali, A., Ouazar, D., Tahayt, A., King, R.W., Vernant, P., Reilinger, R.E., McClusky, S., Sourabit, T., Davila, J.M., Amraoui, N., 2011. New GPS constraints on active deformation along the Africa–Iberia plate boundary. Earth Planet. Sci. Lett. 308, 211–217. https://doi.org/10.1016/j.epsl.2011.05.048.

Lafosse, M., d'Acremont, E., Rabaute, A., Mercier de Lépinay, B., Tahayt, A., Ammar, A., Gorini, C., 2017. Evidence of quaternary transtensive tectonics in the Nekor basin (NE Morocco). Basin Res. 29, 470–489. https://doi.org/10.1111/bre.12185.

Lafosse, M., Gorini, C., Le Roy, P., Alonso, B., d'Acremont, E., Ercilla, G., Rabineau, M., Vázquez, J.T., Rabaute, A., Ammar, A., 2018. Late Pleistocene-Holocene history of a tectonically active segment of the continental margin (Nekor basin, Western Mediterranean, Morocco). Mar. Pet. Geol. 97, 370–389. https://doi.org/10.1016/j. marpetgeo.2018.07.022.

Lafosse, M., d'Acremont, E., Rabaute, A., Estrada, F., Jollivet-Castelot, M., Vazquez, J.T., Galindo-Zaldívar, J., Ercilla, G., Alonso, B., Smit, J., Ammar, A., Gorini, C., 2020. Plio-Quaternary tectonic evolution of the southern margin of the Alboran Basin (Western Mediterranean). Solid Earth 11, 741–765. https://doi.org/10.5194/se-11- 741-2020.

Lafuerza, S., Frigola, J., Canals, M., Jouet, G., Bassetti, M., Sultan, N., Berné, S., 2008. Subseafloor stratigraphic profiling and soil classification from piezocone tests: a case study in the Gulf of Lion (NW Mediterranean Sea): PIEZOCONE STRATIGRAPHIC PROFILING OF THE GULF OF LION. Geochem. Geophys. Geosyst. 9. https://doi.org/ 10.1029/2007GC001845 n/a/n-a.

Liu, S., Hernández-Vida, J.F., Lei, Z., Duarte, D., Chen, H., Wang, C., Lei, Y., Zhuo, H., Huang, S., Zhang, L., Su, M., 2021. Fault-controlled contourite drifts in the southern South China Sea: Tectonic, oceanographic, and conceptual implications. Mar. Geol. 433, 106420. https://doi.org/10.1016/j.margeo.2021.106420.

Lozano, L., Buforn, E., Vicente Cantavella, J., López-Sánchez, C., Victoria Manzando, M., Barco, O., Antón, R., Cabieces, R., Mattesini, M., 2025. Relocation of recent shallow seismic activity in the Alboran Sea (Western Mediterranean Sea): the 2021–2024, 2016, and 2004 Seismic Series. Bull. Seismol. Soc. Am. https://doi.org/ 10.1785/0120240159.

Lunne, T., Berre, T., Strandvik, S., 1998. Sample Disturbance Effects in Deep Water Soil Investigations. In: Presented at the Offshore Site Investigation and Foundation Behaviour: New Frontiers - Proceedings of an International Conference, p. SUT- OSIFB-98-199.

Lunne, T., Powell, J.J.M., Robertson, P.K., 2002. Cone Penetration Testing in Geotechnical Practice, 0 ed. CRC Press. https://doi.org/10.1201/9781482295054.

Maniatis, G., Kurfeß, D., Hampel, A., Heidbach, O., 2009. Slip normalisation on normal faults due to erosion and sedimentation — results from a new three-dimensional numerical model coupling tectonics and landscape evolution. Earth Planet. Sci. Lett. 284, 570–582. https://doi.org/10.1016/j.epsl.2009.05.024.

Martínez-García, A., Rosell-Melé, A., Jaccard, S.L., Geibert, W., Sigman, D.M., Haug, G. H., 2011. Southern Ocean dust-climate coupling over the past four million years. Nature 476, 312–315. https://doi.org/10.1038/nature10310.

Martínez-García, P., Comas, M., Soto, J.I., Lonergan, L., Watts, A.B., 2013. Strike-slip tectonics and basin inversion in the Western Mediterranean: the Post-Mississippi evolution of the Alboran Sea. Basin Res. 25, 361–387. https://doi.org/10.1111/ bre.12005.

Matrat, B., Grimalt, J.O., Lopez-Martinez, C., Cacho, I., Sierro, F.J., Flores, J.A., Zahn, R., Canals, M., Curtis, J.H., Hodell, D.A., 2004. Abrupt Temperature changes in the Western Mediterranean over the past 250,000 years. Science 306, 1762–1765. https://doi.org/10.1126/science.1101706.

McCalpin, J.P., Carver, G.A., 2009. Chapter 5 paleoseismology of compressional tectonic environments. In: International Geophysics. Elsevier, pp. 315–419. https://doi.org/ 10.1016/S0074-6142(09)95005-7.

Medina, F., Cherkaoui, T.-E., 2017. The South-Western Alboran Earthquake Sequence of January–March 2016 and its Associated Coulomb stress changes. OJER 06, 35–54. https://doi.org/10.4236/ojer.2017.61002.

Meyer, A.F.T., Stirling, M.W., Griffin, J.D., Tarling, M.S., Stirling, T.W., Thomsen, J.M., 2025. Paleoseismology of the Long Valley Fault, Central Otago, New Zealand. N. Z. J. Geol. Geophys. 1–8. https://doi.org/10.1080/00288306.2025.2519711.

Mia, M.S., Abdelmeguid, M., Harris, R.A., Elbanna, A.E., 2024. Rupture jumping and seismic complexity in models of earthquake cycles for fault stepovers with off-fault plasticity. Bull. Seismol. Soc. Am. 114, 1466–1480. https://doi.org/10.1785/ 0120230249.

Moreno, A., Cacho, I., Canals, M., Prins, M.A., Sánchez-Goní, M.-F., Grimalt, J.O., Weltje, G.J., 2002. Saharan dust transport and high-latitude glacial climatic variability: the Alboran Sea Record. Quat. Res. 58, 318–328. https://doi.org/ 10.1006/qres.2002.2383.

Neres, M., Carafa, M.M.C., Fernandes, R.M.S., Matias, L., Duarte, J.C., Bara, S., Terrinha, P., 2016. Lithospheric deformation in the Africa-Iberia plate boundary: improved neotectonic modeling testing a basal-driven Alboran plate. JGR Solid Earth 121, 6566–6596. https://doi.org/10.1002/2016JB013012.
Okal, E.A., Synolakis, C.E., 2003. A theoretical comparison of Tsunamis from dislocations and landslides. Pure Appl. Geophys. 160, 2177–2188. https://doi.org/10.1007/s0024-003-2425-x.

Parke, Minshull, Anderson, White, McKenzie, Kuşçu, Bull, Görür, Şengör, 1999. Active faults in the Sea of Marmara, western Turkey, imaged by seismic reflection profiles. Terra Nova 11, 223–227. https://doi.org/10.1046/j.1365-3121.1999.00248.x.

Pouderoux, Hugo, Proust, Jean-Noël, Lamarche, Geoffroy, 2014. Submarine paleoseismology of the northern Hikurangi subduction margin of New Zealand as deduced from Turbidite record since 16 ka. Quat. Sci. Rev. 84, 116–131. ISSN 0277-3791, https://doi.org/10.1016/j.quascirev.2013.11.015.

Reesco, M., Hernández-Molina, F.J., Van Rooij, D., Wâhlin, A., 2014. Contourites and associated sediments controlled by deep-water circulation processes: State-of-the-art and future considerations. Mar. Geol. 352, 111–154. https://doi.org/10.1016/j.margeo.2014.03.011.

Reicherter, K., Becker-Heidmann, P., 2009. Tsunami deposits in the western Mediterranean: remains of the 1522 almeria earthquake? SP 316, 217–235. https://doi.org/10.1144/SP316.14.

Reicherter, K., Hübscher, C., 2007. Evidence for a seafloor rupture of the Carboneras Fault Zone (southern Spain): Relation to the 1522 Almería earthquake? J. Seismol. 11, 15–26. https://doi.org/10.1007/s10950-006-9024-0.

Robertson, P.K., 1990. Soil classification using the cone penetration test. Can. Geotech. J. 27, 151–158. https://doi.org/10.1139/t90-014.

Robertson, P.K., 2009. Interpretation of cone penetration tests — a unified approach. Can. Geotech. J. 46, 1337–1355. https://doi.org/10.1139/T09-065.

Ruiz-Constán, A., Galindo-Zaldívar, J., Pedrera, A., Célérier, B., Marín-Lechado, C., 2011. Stress distribution at the transition from subduction to continental collision (northwestern and central Betic Cordillera): FROM SUBDUCTION TO CONTINENTAL COLLISION. Geochem. Geophys. Geosyst. 12. https://doi.org/10.1029/2011GC003824 n/a/n/a.

Sahal, A., Roger, J., Allgeyer, S., Lemaire, B., Hébert, H., Schindelé, F., Lavigne, F., 2009. The tsunami triggered by the 21 May 2003 Boumerdès-Zemmouri (Algeria) earthquake: field investigations on the French Mediterranean coast and tsunami modelling. Nat. Hazards Earth Syst. Sci. 9, 1823–1834. https://doi.org/10.5194/nhess-9-1823-2009.

Sánchez-Roldán, J.L., Álvarez-Gómez, J.A., Martínez-Díaz, J.J., Herrero-Barbero, P., Perea, H., Cantavella, J.V., Lozano, L., 2024. New 3D Velocity Model (mTAB3D) for absolute Hypocenter Location in Southern Iberia and the Westernmost Mediterranean. Earth Space Sci. 11. https://doi.org/10.1029/2023EA002993

Seibert, C., Feuillet, N., Ratzov, G., Beck, C., Morena, P., Johannes, L., Ducassou, E., Cattaneo, A., Goldfinger, C., Moreno, E., Bieber, A., Bénatre, G., Caron, B., Caron, M., Casse, M., Cavailhes, T., Del Manzo, G., Deschamps, C.E., Desiage, P.A., Duboc, Q., Fauquembergue, K., Ferrant, A., Guyard, H., Jacques, E., Laurencin, M., Leclerc, F., Patton, J., Saurel, J.M., St-Onge, G., Woerther, P., 2024. Sedimentary Records in the Lesser Antilles Fore-Arc Basins Provide Evidence of large late Quaternary Megathrust Earthquakes. Geochem. Geophys. Geosyst. 25. https://doi.org/10.1029/2023GC011152 e2023GC011152.

Selva, J., Lorito, S., Volpe, M., Romano, F., Tonini, R., Perfetti, P., Bernardi, F., Taroni, M., Scala, A., Babeyko, A., Løvholt, F., Gibbons, S.J., Macías, J., Castro, M.J., González-Vida, J.M., Sánchez-Linares, C., Bayraktar, H.B., Basili, R., Maesano, F.E., Tiberti, M.M., Mele, F., Piatanesi, A., Amato, A., 2021. Probabilistic tsunami forecasting for early warning. Nat. Commun. 12, 5677. https://doi.org/10.1038/s41467-021-25815-w.

Serpelloni, E., Bürgmann, R., Anzidei, M., Baldi, P., Mastrolembo Ventura, B., Boschi, E., 2010. Strain accumulation across the Messina Straits and kinematics of Sicily and Calabria from GPS data and dislocation modeling. Earth Planet. Sci. Lett. 298, 347–360. https://doi.org/10.1016/j.epsl.2010.08.005.

Skinner, L.C., McCave, I.N., 2003. Analysis and modelling of gravity- and piston coring based on soil mechanics. Mar. Geol. 199, 181–204. https://doi.org/10.1016/S0025-3227(03)00127-0.

Stefatos, A., Papatheodorou, G., Ferentinos, G., Leeder, M., Collier, R., 2002. Seismic reflection imaging of active offshore faults in the Gulf of Corinth: their seismotectonic significance. Basin Res. 14, 487–502. https://doi.org/10.1046/j.1365-2117.2002.00176.x.

Stich, D., Serpelloni, E., De Lis Mancilla, F., Morales, J., 2006. Kinematics of the Iberia–Maghreb plate contact from seismic moment tensors and GPS observations. Tectonophysics 426, 295–317. https://doi.org/10.1016/j.tecto.2006.08.004.

Stich, D., Martín, R., Morales, J., López-Comino, J.Á., Mancilla, F.d.L., 2020. Slip Partitioning in the 2016 Alboran Sea Earthquake Sequence (Western Mediterranean). Front. Earth Sci. 8, 587356. https://doi.org/10.3389/feart.2020.587356.

Stuiver, M., Reimer, P.J., 1993. Extended<sup>14</sup>C Data Base and revised CALIB 3.0<sup>14</sup> C Age Calibration Program. Radiocarbon 35, 215–230. https://doi.org/10.1017/S0033822200013904.

Sultan, N., Voisset, M., Marsset, B., Marsset, T., Cauquil, E., Colliat, J.-L., 2007. Potential role of compressional structures in generating submarine slope failures in the Niger Delta. Mar. Geol. 237, 169–190. https://doi.org/10.1016/j.margeo.2006.11.002.

Sultan, N., Savoye, B., Jouet, G., Leynaud, D., Cochonat, P., Henry, P., Stegmann, S., Kopf, A., 2010. Investigation of a possible submarine landslide at the Var delta front (Nice continental slope, Southeast France). Can. Geotech. J. 47, 486–496. https://doi.org/10.1139/T09-105.

Sykes, L.R., Menke, W., 2006. Repeat times of large earthquakes: Implications for earthquake mechanics and long-term prediction. Bull. Seismol. Soc. Am. 96, 1569–1596. https://doi.org/10.1785/0120050083.

Tahayt, A., Feigl, K.L., Mourabit, T., Rigo, A., Reilinger, R., McClusky, S., Fadil, A., Berthier, E., Dorbath, L., Serroukh, M., Gomez, F., Ben Sari, D., 2009. The Al Hoceima (Morocco) earthquake of 24 February 2004, analysis and interpretation of data from ENVISAT ASAR and SPOT5 validated by ground-based observations. Remote Sens. Environ. 113, 306–316. https://doi.org/10.1016/j.rse.2008.09.015.

Tendero-Salmerón, V., Lafosse, M., d'Acremont, E., Rabaute, A., Azzouz, O., Ercilla, G., Makkaoui, M., Galindo-Zaldivar, J., 2021. Application of automated throw backstripping method to characterize recent faulting activity migration in the Al Hoceima Bay (Northeast Morocco): Geodynamic implications. Front. Earth Sci. 9. https://doi.org/10.3389/feart.2021.645942.

Trias-Navarro, S., Pena, L.D., De La Fuente, M., Paredes, E., Garcia-Solsona, E., Frigola, J., Català, A., Caruso, A., Lirer, F., Haghipour, N., Pérez-Asensio, J.N., Cacho, I., 2023. Eastern Mediterranean water outflow during the Younger Dryas was twice that of the present day. Commun. Earth Environ. 4, 147. https://doi.org/10.1038/s43247-023-00812-7.

Usami, K., Ikehara, K., Kanamatsu, T., McHugh, C.M., 2018. Supercycle in great earthquake recurrence along the Japan Trench over the last 4000 years. Geosci. Lett. 5. https://doi.org/10.1186/s40562-018-0110-2.

Van Der Woerd, J., Dorbath, C., Ousadou, F., Dorbath, L., Delouis, B., Jacques, E., Tapponnier, P., Hahou, Y., Menzhi, M., Frogneux, M., Haessler, H., 2014. The Al Hoceima Mw 6.4 earthquake of 24 February 2004 and its aftershocks sequence. J. Geodyn. 77, 89–109. https://doi.org/10.1016/j.jog.2013.12.004.

Vernant, P., Fadil, A., Mourabit, T., Ouazar, D., Koulali, A., Davila, J.M., Garate, J., McClusky, S., Reilinger, R., 2010. Geodetic constraints on active tectonics of the Western Mediterranean: Implications for the kinematics and dynamics of the Nubia-Eurasia plate boundary zone. J. Geodyn. 49, 123–129. https://doi.org/10.1016/j.jog.2009.10.007.

Wells, D.L., Coppersmith, K.J., 1994. New empirical relationships among magnitude, rupture length, rupture width, rupture area, and surface displacement. Bull. Seismol. Soc. Am. 84, 974–1002. https://doi.org/10.1785/BSSA0840040974.

Wesson, R.L., 1988. Dynamics of fault creep. J. Geophys. Res. 93, 8929–8951. https://doi.org/10.1029/JB093iB08p08929.