# 1942 Ecuador earthquake

The 1942 Ecuador earthquake or the Guayaquil earthquake occurred on 13 May at 21:13 ECT with a moment magnitude (M$_w$ ) of 7.8–7.9. The earthquake had an epicenter near the coast of Manabí Province, Ecuador. It killed more than 300 people and the total cost of damage was about US$2.5 million. At Guayaquil, 250 km (160 mi) from the epicenter, many reinforced concrete structures in the city were destroyed and high-rise buildings collapsed. At least 100 fatalities were recorded in the city.
The earthquake was caused by movement on a section of the Ecuador–Colombia subduction zone, a seismically active area where the Nazca plate subducts beneath the overriding South American Plate. This subduction zone previously ruptured during a larger earthquake in 1906, and the 1942 event represented a partial re-rupture. The same section that caused the 1942 earthquake would move again in a 2016 earthquake.

## Geology

A subduction zone exists off the coast of Ecuador and Colombia due to oblique convergence between the continental South American plate, and oceanic Nazca plate. Along the Ecuador coast, the subduction zone is divided into three segments based on their seismic rupture history. In 1906, a M$_w$  8.8 earthquake ruptured the northern (470 km (290 mi) long) and middle (150 km (93 mi) long) segments. These individual segments subsequently ruptured during the earthquakes of 1942, 1958 and 1979. A southern segment also exists, measuring 300 km (190 mi) long. The central portion of the subduction zone was also responsible for earthquakes in 1896, 1907, 1942, 1956 and 1998. The rate of convergence between these plates is estimated at 5 to 8 cm (2.0 to 3.1 in) per year.

## Earthquake

The earthquake struck near the coast of Ecuador on 13 May at 21:13 ECT. It measured 7.8–7.9 on the moment magnitude scale, had a hypocenter depth of 20 km (12 mi), and epicenter about 15 km (9.3 mi) west of Pedernales. It was caused by a rupture initiating on the subduction zone at the northern flank of the subducting Carnegie Ridge. The rupture released all of the seismic energy in one episode which lasted 22 seconds. A relocation of the aftershocks and examining their distribution suggested that the earthquake ruptured a section of the subduction zone about 200 km (120 mi) long by 90 km (56 mi) across. Most of the aftershocks were recorded north of the epicenter. Due to the buoyancy of the Carnegie Ridge, it decreases the angle of which the Nazca Plate subducts. As a resut, the portion of the trench is shallower and the coastline is raised. The northern flank also acts as a rupture barrier, preventing seismic ruptures to propagate beyond, as observed during the 1906 and 1942 events which ceased in this area. Since no ruptures can extend past the ridge, this section of the subduction zone experience fewer tsunamis.
The 1942 earthquake was the first event in a sequence of large earthquakes that would re-rupture the Ecuador–Colombia subduction zone, which had already ruptured in 1906. Subsequent events would occur in 1958 and 1979. In 2016, a M$_w$  7.8 earthquake ruptured the portion of the subduction zone that was involved in the 1942 event, north of a 1998 rupture. The 2016 event caused 2 m (6 ft 7 in) of slip on the subduction zone which is indicative of the slip accumulated on the subduction zone while it was locked. The earthquakes of 1942 and 2016 are part of a cycle of repeated earthquakes with an average recurrence interval period of 74 years, indicating the next event may occur in 2090.

## Impact

The earthquake caused more than 300 deaths across Ecuador and US$2.5 million in damage. The city of Guayaquil experienced the worst damage despite its location about 250 km (160 mi) from the epicenter. There, more than 100 people died and numerous high-rise buildings collapsed. Damage was reported in the provinces of Manabí, Guayas, Los Ríos, Esmeraldas, Bolívar and Imbabura.
Most of the city sustained moderate damage, and the reported Mercalli intensity was VI–VII (Strong–Very strong) in many areas. However, in the downtown area, the damage in several reinforced concrete buildings corresponded with IX (Violent). In the central, southern, and western parts of the city, situated on loose soil, the damage was evaluated at VIII (Severe), while areas on harder bedrock experienced VI (Strong) intensity. Forty people were killed by collapsed buildings; the greatest loss of life occurred at the corner of Pichincha and Colón streets when a five-storey clinic collapsed. In the same area, electricity and tram services were disrupted. Three buildings with four or five floors collapsed while others with three floors or more were heavily damaged. The greatest degree of damage occurred on the first floor of these buildings. Fractured columns and walls, toppled facades and walls, and tilting occurred in other buildings.
Three buildings had beams on their first floor so badly damaged that supports had to be installed immediately before they could be repaired or demolished. The location where the strongest intensity was felt in Guayaquil is just west of the Guayas River and south of Cerro Del Carmen. The city was constructed above water-saturated clay and alluvium deposited by the river. This soil condition amplified the seismic waves as it propagated beneath the city which worsened the strength of strong ground motion. Additional damage was reported in the cities of Chone, Portoviejo, Manta, Junín, Calcetan and Pedernales. In the Naranjal Canton, large fissures formed in the ground which allowed a "foamy liquid" to erupt. Many homes and buildings situated along the coast were seriously damaged or destroyed. The shaking was felt as far as the Oriente region in the east and in the border towns of Colombia towards the north. A moderate tsunami was also reported along the coast, causing minor damage and a few fatalities. Additionally, two strong aftershocks rocked the coast of Ecuador, causing more panic. During the night many residents of Guayaquil slept in public parks or in their vehicles. The earthquake also caused disruptions and damage to water infrastructure such as leaks at various places, forcing services to be limited to a few hours at certain times of the day. However, within a week, most pipelines were repaired. Electrical and telephone services were also affected, plunging the city in darkness while in other instances, they were deliverately cut to prevent short circuits and fires.