The complexity of the double earthquake in Venezuela

On the evening of June 24, Venezuela suffered the strongest earthquake in more than a century, causing many buildings to collapse and at least 235 people to die. According to the US Geological Survey (USGS), this is a rare phenomenon called a double earthquake consisting of two large earthquakes. Both earthquakes were centered northwest of the town of Yumare, near the city of Morón and about 160 km west of the Venezuelan capital Caracas. According to Wiredthe earthquakes occurred at depths of 20.3 and 10 km, and were felt in many areas of northern Venezuela and several Caribbean countries.

Theo CNNa double earthquake occurs when two earthquakes of similar magnitude, consecutively, can cause more serious damage than individual earthquakes. In this case, a 7.2 magnitude earthquake shook the area and just 39 seconds later, a 7.5 magnitude earthquake followed. The double earthquake revealed a complex geological structure with three major faults including Boconó (running along the spine of the Andes in Venezuela with a length of about 500 km), El Guayabo (almost parallel to Boconó) and Morón (located in northern Venezuela and the neighboring Caribbean Sea).

Theo Wall Street Journalinitial data shows that the magnitude 7.5 earthquake was more likely to occur near the El Guayabo fault, while the magnitude 7.2 event appears to be closer to the Morón fault. However, due to many uncertain factors, all three faults are considered culprits, potentially even operating simultaneously.

Mark Allen, a professor at Durham University’s Department of Earth Sciences, said June 24’s tremor occurred at the boundary between the Caribbean and South American plates, which is sliding at a rate of about 20 mm/year. In this area, two tectonic plates move horizontally relative to each other, similar to the San Andreas fault in California, USA, creating favorable conditions for generating strike-slip earthquakes. This type of earthquake occurs when two blocks of the Earth’s crust move laterally along a fault and suddenly release stress that has built up over a long period of time.

This type of movement often causes severe damage because it originates at a relatively shallow depth. Unlike subduction earthquakes, which occur when one tectonic plate slides under another, strike-slip earthquakes tend to occur closer to the Earth’s surface. As a result, the released energy travels shorter distances before reaching densely populated areas, increasing the intensity of shaking and the risk of damage.

However, some researchers say more data collected in the coming days could reveal the event was caused by a megaquake instead of a double quake.

According to Judith Hubbard, a scientist at Cornell University, because of the intense shaking, confirming there were two earthquakes from preliminary data could be difficult. A 7.5 magnitude earthquake usually does not occur immediately but starts at one location and propagates along the fault, breaking different sections at different times. In the Venezuela event, the first seismic pulse (responsible for the 7.2 magnitude earthquake) could trigger a domino effect on subsequent pulses, leading to stronger earthquakes.

An earthquake typically lasts about 30-40 seconds, but because the stronger pulse occurs during the shaking of the first pulse, it is difficult to detect in current data. If these were two seismic pulses of a single fault, Hubbard said the event could be equivalent to a 7.6 magnitude earthquake. The USGS preliminary report does not rule out the possibility of one quake triggering the other. Even though they appear close together, the faults behind the earthquakes slide in opposite directions. Satellite data over the next few days could provide further clues about the fault’s movements.

USGS predicts that after earthquakes of this magnitude, seismic activity may continue for days, weeks or even longer. Although the frequency decreases over time, there is still the possibility of strong aftershocks. USGS estimates the final death toll could range from 10,000 to 100,000 people due to factors related to earthquake intensity, construction quality and population density in the affected area.