Chile is a large territory prone to mega earthquakes that cause big tsunamis. Particularly, the country’s central regions – including the Metropolitan Region and the port city of Valparaiso – have historically suffered from multiple large earthquakes. Since the 18th century, at least four earthquakes of a magnitude close or greater than 8.0 Mw have struck Valparaíso: in 1730, 1822, 1906, and 1985.
The earthquake and tsunami of 1730 are the largest of these, with an estimated magnitude of between 9.1 and 9.3 Mw. Shaking and causing damage along 1,000 kilometers of the country, they hugely affected the Valparaiso coast in the early morning of July 8th. Such a disaster occurred 290 years ago.
Today, what we know about this seismic event is the result of scientific research, including numerical modeling, studies of historical chronicles of the time about the earthquake, and the geological evidence of the tsunami, whose waves in Chile could even have exceeded 10 meters high. This mega event generated considerable damage in the most populated cities of that time, such as Valparaíso, Santiago, Concepción (located at that time in what is now Penco city), and La Serena.
Memory and education
Recently, a scientific article was published in the Geoscience journal summarizing the memory and education efforts made in 2019 to make this event public, which had a broad academic and citizen collaboration led by the Integrated Disaster Risk Management Research Centre (CIGIDEN). In this work, entitled as “The 1730 Great Metropolitan Chile Earthquake and Tsunami Commemoration: Joint Efforts to Increase the Country’s Awareness”, it is stated that remembering this disaster is not only a way to make a progressively forgotten seismic event visible, but also “a way to encourage the memory and awareness of the community to be better prepared, and save lives in the future”.
“To make better urban planning and development decisions, and also to promote an immediate evacuation response after a mega earthquake, it is indispensable that people know what had happened in the past, reinforcing risk education and communication, since this event has certain possibilities of recurring in the future,” explains Rodrigo Cienfuegos, one of the paper’s authors and CIGIDEN director. Moreover, there is a mistaken perception that in Valparaiso the bay would not be affected by a tsunami, possibly associated with the fact that no significant damage or flooding was observed after the 1985, 2010, and 2015 earthquakes.
To raise awareness and demystify the misperception of risk, CIGIDEN recreated the 1730 event from mathematical simulation models. Also, along with web designers and developers, CIGIDEN created a virtual space hosted on its website, where it is possible to visualize on a 3D map of the Valparaiso bay, the flood simulation of a tsunami caused by a similar event to the one that occurred in 1730.
“The simulation allows us to observe the rapid arrival of the first waves (less than 20 minutes) and extensive flooding of the Valparaiso plane. In the 1730 event, records are indicating that the flood even reached the foot of the current location of Plaza de La Matriz, in the historic quarter of Valparaíso”, Cienfuegos adds.
The simulation represents the 1730 event in the Valparaiso region, with the propagation and inundation of the tsunami that scientists modeled using the most advanced numerical tools available today. The main objective of these efforts is to allow people to visualize the extent of a tsunami of this magnitude in Valparaiso, in order to understand the potential risk that exists if such an event occurred again.
The most recent studies, the CIGIDEN director adds, indicating that the accumulated seismic energy is sufficient to produce a tsunamigenic earthquake in this area, makes it urgent to reinforce all mitigation and preparedness measures, including population’s immediate self-evacuation after an earthquake that makes it difficult to stand and that lasts more than 1 minute. Furthermore, “our center has already formally submitted to the authorities studies that emphasize the urgency of implementing vertical evacuation strategies, especially in the city of Viña del Mar, due to the high population density near the coast and the Marga-Marga estuary,” Cienfuegos says.
According to the authors of the scientific publication, the danger that a similar earthquake and tsunami represent for the central coastal zone today is enormous. It poses a greater risk, due to the high exposure level generated by urban development in Valparaíso and Viña del Mar, which did not consider that possibly a tsunami like the one in 1730 could affect them. Today, there is a large quantity of population, services, and critical infrastructure located in the flood zone.
Additionally, the authors of the Geoscience paper say, “Valparaíso and Viña del Mar are tourist areas visited by a high number of foreigners and people who do not live on the coast”. Only in the summertime, the floating population can exceed by 30% the usual population in Valparaíso, Viña and Concón cities. “Many tourists, especially foreigners, have limited education about tsunami threat and how to face it. That is why reinforcing educational and informational plans for all those who visit our country should be a priority. Also, adapting the protocols to the pandemic context in which we find ourselves is a task that must be addressed,” Rodrigo Cienfuegos concludes.