1797 Riobamba earthquake
Encyclopedia
The 1797 Riobamba earthquake occurred at 12:30 UTC
on 4 February. It devastated the city of Riobamba
and many other cities in the Interandean valley, causing up to 40,000 casualties. It is estimated that seismic intensities in the epicentral
area reached at least XI on the Mercalli scale, and that the earthquake had a magnitude
of 8.3, the most powerful historical event known in Ecuador. The earthquake was studied by Alexander von Humboldt
, when he visited the area in 1801/2.
of Ecuador is dominated by the effects of the subduction
of the Nazca Plate
beneath the South American Plate
. The main NNE-SSW trending fault systems show a mixture of dextral (right lateral) strike-slip faulting and reverse faulting. In addition to these fault that run parallel to the Andes in Ecuador, there are two important SW-NE trending dextral fault systems, the Pallatanga fault and the Chingual fault. The Pallatanga fault runs close to the epicenter
and movement on this fault has been suggested as the cause of the earthquake, although there is no clear surface break supporting such recent movement.
in the north to more than 60 km south of Riobamba, including the cities of Guaranda
, Ambato, Latacunga
and the towns of Saquisilí
and Baños. Riobamba and the town of Quero
were both destroyed by landslides. At the foot of the Tungurahua
volcano, the Pastaza River
was dammed by landslides for up to eighty days.
Humboldt's analysis of this earthquake relied on anecdotal accounts that he gathered during his visit. Some of the observations such as "the bodies of many of the inhabitants were found to have been hurled to Cullca, a hill several hundred feet in height and on the opposite side of the river Lican", are not credible. He gave a figure of thirty to forty thousand for the number of casualties, while some more recent estimates give figures as low as six thousand.
.
Coordinated Universal Time
Coordinated Universal Time is the primary time standard by which the world regulates clocks and time. It is one of several closely related successors to Greenwich Mean Time. Computer servers, online services and other entities that rely on having a universally accepted time use UTC for that purpose...
on 4 February. It devastated the city of Riobamba
Riobamba
Riobamba is the capital of the Chimborazo Province in central Ecuador, which is located at the Chambo River Valley of the Andes. It is south of Ecuador's capital Quito and located at 2754 m on the Avenue of the Volcanoes...
and many other cities in the Interandean valley, causing up to 40,000 casualties. It is estimated that seismic intensities in the epicentral
Epicenter
The epicenter or epicentre is the point on the Earth's surface that is directly above the hypocenter or focus, the point where an earthquake or underground explosion originates...
area reached at least XI on the Mercalli scale, and that the earthquake had a magnitude
Richter magnitude scale
The expression Richter magnitude scale refers to a number of ways to assign a single number to quantify the energy contained in an earthquake....
of 8.3, the most powerful historical event known in Ecuador. The earthquake was studied by Alexander von Humboldt
Alexander von Humboldt
Friedrich Wilhelm Heinrich Alexander Freiherr von Humboldt was a German naturalist and explorer, and the younger brother of the Prussian minister, philosopher and linguist Wilhelm von Humboldt...
, when he visited the area in 1801/2.
Tectonic setting
The active tectonicsTectonics
Tectonics is a field of study within geology concerned generally with the structures within the lithosphere of the Earth and particularly with the forces and movements that have operated in a region to create these structures.Tectonics is concerned with the orogenies and tectonic development of...
of Ecuador is dominated by the effects of the subduction
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
of the Nazca Plate
Nazca Plate
]The Nazca Plate, named after the Nazca region of southern Peru, is an oceanic tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction along the Peru-Chile Trench of the Nazca Plate under the South American Plate is largely responsible for the...
beneath the South American Plate
South American Plate
The South American Plate is a continental tectonic plate which includes the continent of South America and also a sizeable region of the Atlantic Ocean seabed extending eastward to the Mid-Atlantic Ridge....
. The main NNE-SSW trending fault systems show a mixture of dextral (right lateral) strike-slip faulting and reverse faulting. In addition to these fault that run parallel to the Andes in Ecuador, there are two important SW-NE trending dextral fault systems, the Pallatanga fault and the Chingual fault. The Pallatanga fault runs close to the epicenter
Epicenter
The epicenter or epicentre is the point on the Earth's surface that is directly above the hypocenter or focus, the point where an earthquake or underground explosion originates...
and movement on this fault has been suggested as the cause of the earthquake, although there is no clear surface break supporting such recent movement.
Damage
The area of significant damage (Intensity ≥VII) extended from QuitoQuito
San Francisco de Quito, most often called Quito , is the capital city of Ecuador in northwestern South America. It is located in north-central Ecuador in the Guayllabamba river basin, on the eastern slopes of Pichincha, an active stratovolcano in the Andes mountains...
in the north to more than 60 km south of Riobamba, including the cities of Guaranda
Guaranda
San Pedro de Guaranda is a city in central Ecuador. It is the capital of Bolívar, a province located in the Andes mountains. The city has is connected by road with other hubs including, Riobamba, Babahoyo and Ambato....
, Ambato, Latacunga
Latacunga
Latacunga is a plateau town of Ecuador, capital of the Cotopaxi Province, south of Quito, near the confluence of the Alaques and Cutuchi rivers to form the Patate, the headstream of the Pastaza. At the time of census 2001 Latacunga had 51,689 inhabitants, largely mestizo and indigenous.Latacunga...
and the towns of Saquisilí
Saquisilí
Saquisilí is a town in the Cotopaxi Province of Ecuador. It is the seat of the Saquisilí Canton.Sasquisilí is located about 25 minutes from Latacunga and 2.5 hours from Quito. The town, located off the Pan-American Highway, is best known for the local market held in its eight plazas on Thursdays...
and Baños. Riobamba and the town of Quero
Santiago de Quero
Santiago de Quero or simply Quero is a location in the Tungurahua Province, Ecuador. It is the seat of the Quero Canton.- References :* * - External links :*...
were both destroyed by landslides. At the foot of the Tungurahua
Tungurahua
Tungurahua, , rahua : "Throat of Fire" or from Panzaleo) is an active stratovolcano located in the Cordillera Oriental of Ecuador. The volcano gives its name to the province of Tungurahua...
volcano, the Pastaza River
Pastaza River
The Pastaza is a large tributary to the Amazon River.It has its headwaters in the province of Tungurahua, where the Tambo River joins the Latacunga River, near the foot of the Volcano Tungurahua, flowing south-east towards the Amazon Basin...
was dammed by landslides for up to eighty days.
Humboldt's analysis of this earthquake relied on anecdotal accounts that he gathered during his visit. Some of the observations such as "the bodies of many of the inhabitants were found to have been hurled to Cullca, a hill several hundred feet in height and on the opposite side of the river Lican", are not credible. He gave a figure of thirty to forty thousand for the number of casualties, while some more recent estimates give figures as low as six thousand.
Characteristics
The shaking lasted for three to four minutes. The estimated rupture length for the earthquake is 70.3 km, with a fault azimuth of 067°.Aftermath
The city of Riobamba was rebuilt nearly 20 km northeast of its original site, now occupied by the small town of CajabambaCajabamba, Ecuador
Cajabamba is a location in the Chimborazo Province, Ecuador. It is the seat of the Colta Canton.- References :* * - External links :* *...
.