The reasons why two earthquakes of equal magnitude in Venezuela and Panama caused such different damage

The magnitude 7.5 earthquake in Panama affected 188 structures in non-urban areas, while the earthquakes in Venezuela caused severe damage to thousands of homes in populated areas. (AP Photo/Aris Mariota)The earthquakes in Venezuela and Panama had similar magnitudes, but their effects cannot be compared based on that figure alone: the terrain, the distance to the epicenter, the fault rupture, and the vulnerability of the buildings determine the level of damage. While Venezuela recorded two consecutive earthquakes of magnitude 7.2 and 7.5 in a densely populated area, Panama faced a single magnitude 7.5 event in a non-urban area, with damage reported in 188 structures and no fatalities so far, according to La Prensa. The Panamanian earthquake, which occurred on Friday, October 9, was followed by more than 100 aftershocks. In Venezuela, the quakes left 14,239 homes with moderate damage and 11,000 with severe damage, in areas where soft soils can intensify the shaking that reaches buildings. These differences were addressed a month before the Panamanian earthquake by engineers and researchers Óscar Ramírez and Ramiro Vargas during the forum Engineering and Seismic Risk: Building a Resilient Panama, organized by the Technological University of Panama. Ramírez explained that magnitude and distance to the epicenter are not enough to anticipate the consequences of an earthquake. The depth of the focus, the way a fault ruptures, the propagation of the waves, the type of soil, and the properties of each building all play a role in the perceived intensity and the damage. Vargas distinguished between hazard and vulnerability. The former depends on the seismic activity of a territory; the latter expresses a structure's propensity to suffer damage and can be reduced through engineering interventions. The depth of the focus, the propagation of the waves, and the type of soil determine the level of damage from an earthquake beyond its magnitude. EFE/ Raúl Martínez Seismic waves travel through rock and cross soil deposits before reaching a building. The properties of those materials can modify and amplify the motion that the structure receives. Ramírez compared areas such as Paitilla and Punta Pacífica, where rock is found close to the surface, with Costa del Este and Santa María, which are built on deposits of compressible clays. The same structural solution does not necessarily work the same way on both types of terrain. Soil classification alone is not enough either. The final response depends on how it interacts with the mass, stiffness, and damping capacity of each building, which is why two structures in the same location can move differently. People can also experience an earthquake differently depending on the floor they are on. Each structure has its own vibration characteristics, and that condition can coincide with that of the ground. This phenomenon is known as resonance: it occurs when the vibrations of the soil and the building are close and the displacement increases. Ramírez summarized it this way: "When you place a flexible structure on soft soil, the structure will amplify its displacement, but substantially." A couple observes the damage to a building affected after the earthquake that shook Panama's Pacific coast (Photo by MARTIN BERNETTI / AFP). The height of a building does not by itself define its vulnerability. A low building can register greater accelerations than a tower, while a tall, flexible structure can suffer significant displacements under certain ground conditions. Panama's tallest buildings are founded on rock through piles or deep excavations. These foundations must be designed to withstand both vertical loads, such as furniture and people, and the lateral forces caused by an earthquake. Earthquake-resistant design does not seek for a building to remain intact under any shaking. Its goal is for it to be able to deform, dissipate energy, and maintain its stability. Ductility allows some elements to exceed their elastic behavior and concentrate expected damage in specific areas. To achieve this, concrete confinement, steel anchoring, and proper connections between beams and columns are required; a greater amount of reinforcement does not by itself guarantee safe performance. Single-family housing accounts for a significant portion of Panama's seismic exposure. According to the 2023 Census, these buildings exceed one million units and represent about 86% of the total housing stock. Renovations and additions can weaken a house when there are missing beams and columns that tie the walls together, poorly executed connections, or a poor distribution of the walls. The walls must act as an integrated unit, with continuous ties, placement in both directions, and reinforcements anchored to the foundations. Emergency personnel cordoned off a damaged building and a vehicle covered in debris after the earthquake in Panama. (Photo by MARTIN BERNETTI / AFP)The expanded metropolitan area, comprising Panama, San Miguelito, Arraiján, La Chorrera, and Colón, is home to about 2.2 million inhabitants. If sectors in the western part of the country are included, more than 55% of Panama's population lives in areas of high seismic hazard, Vargas estimated. Construction on unstable slopes constitutes another focus of risk. The engineer mentioned areas of San Miguelito, Arraiján, and Chiriquí, where landslides during the rainy season reveal conditions that must also be analyzed in the event of an earthquake. A seismic event can alter the stability and strength of sloped terrain, with direct consequences for the homes built on it. It can also cause liquefaction in water-saturated sandy soils, a phenomenon that reduces their load-bearing capacity. Vargas recalled that liquefaction occurred in El Empalme, in Changuinola, during the 1991 earthquake. He questioned the fact that housing projects were later developed in areas where that hazard had already been identified. Geotechnical studies make it possible to determine the strength of the soil and estimate potential settlements. Against the idea that they increase the cost of a project, Vargas warned: "It is more expensive when people die, it is more expensive to come and repair."