## 2 Archaeology and Archaeoseismology of _Baelo Claudia_
The old town of Belon (described by [PERSON]) was nearly destroyed and buried by a thick \"demolition horizon\" above which a new monumental zone (Forum, Basilica, Theatre, Temples, etc.) was rebuilt; additionally, some parts of the city wall damaged by the earthquake were repaired or reinforced [9]. This new city experienced a period of prosperity, including the construction of many garum fishing factories and the enlargement and monumentalizing of the eastern necroolis of the city [25,26]. Evidence of the second earthquake, which occurred during the late fourth century CE (365-395 AD), is largely preserved in the present architectural remains of the archaeological site. Seismic damage is visible in walls, columns, arches and pavements, that is, in both vertical and horizontal structures, which led to the 2D and 3D geometrical study of the deformations by means of the application of a typical analysis of structural geology [13,16,19]. All the preserved deformations can be catalogued as representative _\"Earthquake Archaeological Effects\"_ (EAEs) according to the classification of [18,20]. These EAEs include: (**a**) fractures, folds and pop-up structures in pavements; (**b**) strain structures generated by permanent ground deformations, such as tilted, displaced, folded or  
Figure 2: Paleogeography of _Baelo Claudia_ (after [11,24]). (1) Betic Substratum (Almarchal Fm. Cretaceous–Eocene); (2) and (3) Pleistocene marine terraces; (4) Post-Roman colluvium; (5) Beach barrier (c. 4 ka BP); (6) Roman spit-bar and beach deposits; (7) Lagoon and river coastal floodplains; (8) Modern fluvial terraces; (9) Active channels; (10) Paleo-channels; (11) Roman buildings; (12) Harbor moorings; (13) submerged ashlars and blocks; (14) Scarps; (15) Flooded areas, late fourth century CE. S1–S5, boreholes [9]; A1–A5, sample sites [12]; R1–R4, sample sites [10]; K1–K11, boreholes [11]; P1–P3, tsunami sample sites [24]. collapsed walls and shock breakouts in flagstones; and (c) strain structures generated by transient seismic shaking, such as penetrative and conjugated (x-cross) fractures in masonry blocks, oriented fallen columns, rotated and displaced masonry blocks in walls and drums, dropped key stones in arches, folded steps and curbs, block impact marks in pavements and dipping broken corners in masonry blocks. The geological analyses of this set of different EAEs indicate an oriented damage of seismic origin, indicating a predominant NE-SW deformation of the ground congruent with a seismic source (fault) located to the SW of the city around the Bolonia Bay (Figure 1). Geological and geophysical analyses indicate that the NE-SE Cabo de Garcia Fault (CGF) or the set of NNE-SSW normal faults identified by the German Scientific Ship _\"Meteor\"_ within the Bay may be the suspected seismogenic source for this ancient earthquake [13, 15]. This second earthquake was followed by a tsunami, probably of local origin since there is no contemporary sedimentary evidence in other key studied locations around the Bolonia Bay [11, 24], which is in accordance with the local seismic sources mentioned above. This destructive event was first documented within the city by [PERSON] et al. [10], reporting its sedimentary signals in the _Decumanus maximus_ and the _littoral ternas_, which retained a large amount of tsunami backwash deposits archaeologically dated to the late fourth century. More recent studies document this tsunami layer in several sectors inside and outside the city walls, in the eastern necroolis [25] and within the adjacent ancient lagoonal area [11]. The tsunami layer is a dark, cohesive sandy deposit (28 to 52 cm thick) containing fragments of pottery, fish and animal bones, glassware and bricks, as well as large boulders of masonry blocks and column drums washed away by the tsunami.