Tide gauge observations of the Indian Ocean tsunami, December 26, 2004, at the Río de la Plata estuary, Argentina

DRAGANI, WALTER; D'ONOFRIO, ENRIQUE; MEDIAVILLA, DERNIS; GRISMEYER, WALTER; FIORE, MONICA

The Tsunami Threat - Research and Technology

INTECH

Lugar: Rijeka; Año: 2011; p. 355 - 370

The aim of this work is to report the first description on water level oscillations at the Río de la Plata (RDP) estuary (35°S, 56°W) associated to a tsunami generated as a response to the magnitude 9.3 earthquake centered off the west coast of northern Sumatra (3.307°N, 95.947°E) on December 26, 2004 at 00:59 UTC. Water level records gathered at several tide gauge stations located at the RDP estuary and at the adjacent continental shelf were filtered and analyzed. The first arrivals were measured at Mar del Plata and 33 min later at Santa Teresita (located 200 km northeastward Mar del Plata and 30 km southward the RDP mouth). Maximum wave heights observed were 0.27 and 0.15 at Santa Teresita and Mar del Plata, respectively, and wave periods were detected in the range from 20 to 120 min. At the RDP estuary, the first arrival was detected at Punta Indio (located at the outer RDP), later at Spar Brasileira (at the middle RDP, with a maximum wave height of 0.20 m) and, finally, the tsunami wave was recorded at Buenos Aires (at the inner RDP) with a maximum wave height of 0.08 m. The tsunami travel time, from the outer to the inner RDP, was 7 h 40 min. The wave presented a remarkable temporal variability in amplitude and period immediately following tsunami wave arrival. A numerical modeling was undertaken to study the tsunami wave propagation, transformation, amplification and attenuation along the continental shelf and RDP estuary, from the continental slope to the upper RDP. The validation of this model was carried out by comparing the recorded and simulated maximum amplitudes. From numerical simulations it can be seen that maximum amplifications were observed at Santa Teresita because the wave propagates almost without refracting and the shoaling effect was highly significant there. On the other hand, the tsunami propagation was highly affected by the bathymetry and the wave amplitude was significantly attenuated at Buenos Aires, located at the inner RDP. Even though this perturbation reached only 0.08 m at the inner RDP, before the Sumatra earthquake, a tsunami wave has never been observed in this estuary.