[11] Chilean seismologists, including Sergio Barrientos from the University of Chile Seismological Service, had suggested that the absence of an aftershock greater than magnitude 6 following the 27 February quake indicated that there remained energy with the potential to be released.

[1] Later in 2010, University of Chile Seismologist Sergio Barrientos stated that the earthquakes were produced inside the South American plate.

[17] On 15 March 2010, seismologist Mario Pardo from the University of Chile Seismological Service ruled out that Pichilemu was experiencing a seismic swarm, after public concerns about the continued aftershocks in the area;[18] as of that date, more than 50 aftershocks had occurred in the area, the strongest of them measuring 6.7 in the moment magnitude scale, minutes after the initial quake.

[21] The earthquakes took place minutes before the new President of Chile, Sebastián Piñera, was sworn in, at about 12:15 local time, at the Chilean congress in Valparaíso, where the shaking was clearly felt.

[26][27] Presidents Néstor Kirchner of Argentina, Evo Morales of Bolivia, Álvaro Uribe of Colombia, Rafael Correa of Ecuador, and Fernando Lugo of Paraguay were present at the ceremony, but television footage showed that the inauguration was not interrupted, even though there was a tsunami warning in place;[25][28] however, it was reported the ceremony was concluded more quickly than planned.

[17] President Piñera cancelled the ceremonial lunch with his visitors and traveled to Rancagua, one of the cities most affected by the earthquakes;[17] Piñera subsequently declared a catastrophe state in O'Higgins Region as a result of the earthquakes, and appointed Army General Antonio Yackcich as Area Commander in Chief (Jefe de Plaza) for the region, while he was visiting Rancagua that day.

[29][30] The declaration meant that "the military would occupy the area to keep order and prevent the kind of looting that occurred in Concepción during the first two to three days after last month's quake", according to The New York Times.

[32] Half an hour after the first earthquake, the Hydrographic and Oceanographic Service of the Chilean Navy (Servicio Hidrográfico y Oceanográfico de la Armada, SHOA) issued a tsunami warning for the area between Coquimbo and Los Lagos regions, as a way of "keeping people protected" against the possible occurrence of new tsunamis.

[34] Following the tsunami alert, thousands of residents of central Pichilemu fled to La Cruz Hill, with some of them staying there for several days,[35][36] and received advice from members of the Army.

[39] According to a preliminary report by the National Office of Emergency of the Interior Ministry (Oficina Nacional de Emergencias del Ministerio del Interior, ONEMI) on 11 March 2010, only 'small waves, without any [special] kind of characteristics' were seen in the area surrounding Pichilemu,[40] while the USGS reported a small tsunami, with sea wave heights of 16 centimetres (0.525 ft) at Valparaíso, and 29 centimetres (0.951 ft) at San Antonio.

[48] In Nilahue Barahona, a village near the town of Pumanque, electric cables fell to the ground during the earthquake, causing a fire that burned 65 hectares (160 acres) of a pine, eucalyptus and grassland forest.

[49] The earthquake was also reported to have been felt in Mendoza,[50] Bariloche, Córdoba, San Rafael, Buenos Aires, Montevideo, and Asunción.

[53] A United States Geological Survey summary of the earthquakes reported damage at Rancagua,[1] 177 kilometers northeast of Pichilemu.

[57] The National Emergencies Office (ONEMI) reported that the aftershock was felt most strongly in Talca, 258 kilometres (160 mi) south of Santiago, and that there were no casualties, only some telephone lines had collapsed.

: Movido cambio de mando se vivió en el país ante nuevas réplicas del terremoto") on 11 March;[17] five days later, local newspaper El Expreso de la Costa published an interview with Mario Pardo, seismologist in charge of the geophysics department of the University of Chile, who recommended people of Pichilemu to "try to remain calm, the worst already happened".

[66] Previously, after the 27 February earthquake, Entre Olas did not stop broadcasting either, despite there was a power outage that lasted for several days.

[67] Nationally distributed newspaper El Mercurio published on its 12 March 2010 main page the headline "6.9 [magnitude] aftershock marks the most seismic day after the earthquake" ("Réplica de 6,9° marca el día más sísmico post terremoto"), adding that "[s]eventeen of the twenty seisms that occurred yesterday [11 March] in central-southern Chile had their epicentre in Pichilemu, Region of O'Higgins, which was declared in Disaster State yesterday.

[43] The New York Times included on their 12 March 2010 main page a photograph of Presidents Fernando Lugo of Paraguay and Rafael Correa of Ecuador "re-acting to an aftershock felt Thursday [11 March] in Valparaíso, Chile, the strongest since the devastating Feb. 27 earthquake"; the photograph was followed by the headline "For Chile, More Aftershocks, and an Inauguration".