As two powerful earthquakes hit Venezuela, west of Caracas, in quick succession on Wednesday, the country’s capital sustained extensive damage.

Authorities were continuing to search for people under the rubble of collapsed buildings on Friday as 235 people were confirmed to have been killed, with 4,300 more injured.

Here is more about why Caracas has sustained so much damage.

How badly damaged is Caracas?

A magnitude 7.2 earthquake struck about 160km (100 miles) west of Caracas, followed less than a minute later by a magnitude 7.5 tremor, the strongest since 1900, according to the US Geological Survey (USGS).

Jorge Rodriguez, head of Venezuela’s national assembly and brother of interim President Delcy Rodriguez, said earlier in the day that 200 people had been trapped, with 250 buildings damaged or destroyed nationwide.

In Caracas and nearby coastal areas, at least eight hospitals, the headquarters of the Venezuelan Red Cross and the French embassy were among buildings reported to have been badly damaged.

Initial assessments released on Thursday put the estimated economic damage at between 1 and 7 percent of Venezuela’s $111bn gross domestic product (GDP). Authorities have not yet provided a separate estimate for losses in the capital.

However, the heaviest damage has been reported in Caracas itself, Al Jazeera’s Teresa Bo, reporting from Bogota in neighbouring Colombia, said on Thursday.

Public infrastructure was also heavily damaged, with acting President Rodriguez reporting power outages in Caracas.

Health Minister Carlos Alvarado said late on Thursday that 235 people had been confirmed dead at medical centres across Venezuela. He also told state media that about 4,300 people had been reported injured so far. Hundreds more are feared trapped or missing under the rubble.

How badly has the city been damaged in previous earthquakes?

This is not the first time Caracas has suffered heavy damage in an earthquake.

In 1812, a powerful earthquake roiled the cities of Merida and Caracas, killing about 30,000 people, according to the USGS. The tremors caused near-total destruction of Caracas’s colonial architecture, flattening homes, churches and public institutions.

In 1967, another earthquake hit the city, causing several high-rise buildings to collapse and killing 240 people.

Why has Caracas been so hard-hit?

Venezuela has a long history of devastating earthquakes because it is located along the boundary between the Caribbean and South American tectonic plates.

Caracas is also in a deep sedimentary basin, which amplifies the seismic waves from earthquakes, Vashan Wright, a geophysicist at the University of California in San Diego, told Al Jazeera.

Another reason Caracas is so vulnerable to damage from earthquakes is that its buildings and infrastructure are not specifically designed to withstand tremors and are often standing on insecure ground.

Al Jazeera’s Teresa Bo said the heaviest damage in Caracas occurred in the Altamira district, where emergency crews pulled survivors from the rubble of a 22-storey building while relatives searched for missing family members. Officials said they are still assessing the full extent of the destruction.

“For example, in the [hard-hit] area of Altamira in Caracas, many of the buildings that collapsed are built on sediments, and this makes them much more vulnerable to seismic waves,” Bo said.

“Also, there’s lots of informal housing in several areas across the country, and those types of buildings are not prepared to sustain very strong earthquakes,” she added.

Adequate urban planning and building codes, which incorporate seismic activity, require substantial funding, which Venezuela can ill afford as it has long been subject to heavy sanctions from the United States and other Western countries.

While some sanctions have been lifted since the US abducted former President Nicolas Maduro in a military strike on Caracas in January and he was replaced by Rodriguez, Caracas is still grappling with the effects of decades of underinvestment.

Another issue for Caracas is that at about 7.8km, the earthquakes were shallow, which means they were more destructive than deeper quakes of the same magnitude would have been.

In deeper earthquakes, much of the energy dissipates as it moves through layers of rock. By contrast, shallow ones release their energy closer to the ground, producing stronger shaking and greater damage in populated areas.

How many people live in informal housing in Caracas?

People living in informal housing are more at risk than others during earthquakes because low-cost, self-built housing structures, often built on hillsides and other slopes, are not resilient against tremors.

The slums in Caracas are known as barrios and are densely populated, lacking proper infrastructure. They comprise self-constructed housing or structures built with unreinforced cinderblocks or bricks, often without formal foundations or steel reinforcement, mostly on the mountainous hillsides surrounding the capital.

The lack of proper urban planning, coupled with construction on steep slopes, makes the barrios vulnerable to natural disasters.

While there is no official figure for the number of Venezuelans living in informal settlements in Caracas, academic estimates suggest they account for 40 to 50 percent of the city’s nearly five million residents.

According to the latest National Survey of Living Conditions (ENCOVI), about 55 percent of Venezuelans are living in poverty.

Which countries are better prepared for earthquakes?

Many parts of the world have adapted infrastructure with seismic engineering. Many earthquake-prone countries now plan and construct buildings with damage mitigation from tremors in mind.

Japan, one of the most quake-prone nations in the world, has strict building codes, which means many structures survive shaking that would devastate poorly built homes in parts of Indonesia or Central America. In most inland earthquakes, the majority of deaths and injuries are caused when poorly built structures collapse rather than by the shaking itself.

Japan has made enormous public investments in seismic research and has superior access to advanced engineering technologies like base isolation, which involves the installation of massive steel or rubber shock absorbers beneath the foundations of buildings.

This is why global deaths and destruction from earthquakes have reduced in the past decades. For instance, in 1556, the deadliest earthquake in recorded history in China’s Shaanxi killed about 830,000 people. In 2023, an earthquake hit northwestern China near the Shaanxi province, killing 127 people.