  A recent statistical analysis of the relationship between tides and seismic
activity in Colombia has suggested the existence of correlation anomalies for
the case of intermediate depth events in the Bucaramanga nest and the Cauca
cluster (Moncayo et al., 2019). In this work, we explore in detail the
hypothesis that tides may be triggering seismic activity in these regions and
extend the analysis to two other seismic clusters in northern-central South
America, specifically in the areas of El Puyo (Ecuador) and Pucallpa (Peru).
For this purpose, we use the available focal mechanism information for seismic
events at these locations, and calculate for each event the Tidal Coulomb
Failure Stress (TCFS) as obtained from estimations of the tidal strain tensor.
Tidal strains are computed considering the Earth body tides and the effect of
the ocean tidal loading. Since our purpose is to elucidate the role of tides in
earthquake nucleation, calculations of the TCFS are conducted not only for the
time of earthquake, but also for the time of the closest maximum strain within
a window of a few hours before the events. Our results tend to support the
hypothesis that tidal stresses are contributing to earthquake generation in all
the studied areas; this trend is especially stronger when TCFS are calculated
at pre-earthquake times. The physical explanation for the positive contribution
of tides to earthquake triggering in intermediate depth clusters may lie in the
fact that a wide diversity of fault plane orientations is possible within a
relatively small volume of subducted lithosphere, so making the tides more
likely to help loosening up the blocks at the fault plane to promote slip.
