Why Venezuela’s Second Earthquake Was So Damaging to Buildings

为什么委内瑞拉的第二次地震对建筑物造成了如此严重的破坏

Verónica Cañas barely had time to grab her 6-year-old son and put on her shoes before running out of her apartment in Caracas. As she ran down the stairs, the walls began to crack and part of the facade started to crumble. A few kilometers away in Altamira, 50-year-old Eduardo Burger watched as one building swayed while another fell apart. 维罗妮卡·卡尼亚斯（Verónica Cañas）几乎没有时间抱起她6岁的儿子并穿上鞋子，就冲出了她在加拉加斯的公寓。当她跑下楼梯时，墙壁开始开裂，部分外墙开始坍塌。几公里外的阿尔塔米拉（Altamira），50岁的爱德华多·伯格（Eduardo Burger）目睹了一栋建筑在摇晃，而另一栋则彻底倒塌。

Neither of them knew that this was not just a single terrible earthquake but instead a rare phenomenon. On June 24, Venezuela experienced a seismic doublet that saw earthquakes of magnitude 7.2 and 7.5 occur just 39 seconds apart. The first tremor occurred with its epicenter in Yaracuy. Just a few seconds later, an even more intense earthquake shook the same region again. 他们两人都不知道，这不仅仅是一次可怕的地震，而是一种罕见的现象。6月24日，委内瑞拉经历了一次“地震双重奏”（seismic doublet），两次震级分别为7.2级和7.5级的地震仅相隔39秒发生。第一次地震的震中位于亚拉奎州（Yaracuy）。仅仅几秒钟后，一场强度更大的地震再次震动了同一地区。

Both occurred at a shallow depth of between 10 and 20 kilometers (6 and 12 miles), which caused the energy to reach the surface with greater intensity and allowed the seismic waves to be felt as far away as Colombia, northern Brazil, and several Caribbean islands such as Aruba, Bonaire, and Curaçao. While one alone would’ve caused damaged, it was the one-two punch that created the conditions that brought down so many buildings and have made it hard to rescue survivors as the death toll mounts. 两次地震的震源深度都很浅，在10到20公里（6到12英里）之间，这使得能量以更大的强度到达地表，并使远至哥伦比亚、巴西北部以及阿鲁巴、博内尔和库拉索等多个加勒比岛屿都能感受到地震波。虽然单次地震就会造成破坏，但这种“连环重击”创造了导致大量建筑物倒塌的条件，并随着死亡人数的增加，使得救援幸存者变得更加困难。

The Technical Explanation: Tectonic Plates, Damage, and Resonance

技术解释：构造板块、破坏与共振

“The dining room table started to shake … We thought it was a tremor; then it started shaking much more violently. The walls were cracking, and pieces of the ceiling were falling. We thought it was going to collapse on top of us,” Cañas says. “餐桌开始晃动……我们以为只是轻微震动；然后它开始剧烈摇晃。墙壁开裂，天花板碎片不断掉落。我们以为它会塌在我们身上，”卡尼亚斯说。

She and her family managed to make it to a sports field across from the building, where other neighbors were beginning to gather. There, they were hit by another tremor. 她和家人设法跑到了大楼对面的一块运动场，其他邻居也开始聚集在那里。就在那里，他们遭遇了第二次震动。

“We all hugged each other, terrified, because we’re not used to this. In Mexico and Chile, there’s an earthquake-preparedness culture, and people are already prepared when an alarm goes off or they feel certain movements, but we aren’t,” she says. “我们都惊恐地拥抱在一起，因为我们不习惯这种情况。在墨西哥和智利，有一种地震防灾文化，当警报响起或感觉到震动时，人们已经做好了准备，但我们没有，”她说。

Cañas’ experience highlights one of the main differences between Venezuela and other countries with higher seismic activity. Although the country lies at the boundary between the Caribbean Plate and the South American Plate, earthquakes of this magnitude are relatively rare. 卡尼亚斯的经历凸显了委内瑞拉与其他地震高发国家之间的主要区别之一。尽管该国位于加勒比板块和南美板块的交界处，但这种震级的地震相对罕见。

Alan Damián Sánchez Pulido, a civil engineer from Mexico’s Ibero-American University and a specialist in structural damage assessment, explains that the plates’ positions and movements are why earthquakes aren’t as common as they are in other regions—and why they’re so powerful when they do occur. 墨西哥伊比利亚美洲大学的土木工程师、结构损伤评估专家艾伦·达米安·桑切斯·普利多（Alan Damián Sánchez Pulido）解释说，板块的位置和运动方式决定了为什么这里的地震不像其他地区那样频繁，以及为什么一旦发生，威力会如此巨大。

“In Venezuela, the interaction between the Caribbean and South American plates involves parallel movement; that is what may have caused two earthquakes of considerable magnitude to occur in such quick succession,” he notes. “在委内瑞拉，加勒比板块和南美板块之间的相互作用涉及平行运动；这可能就是导致两次相当震级的地震在如此短的时间内接连发生的原因，”他指出。

Unlike Mexico, where the Cocos Plate subducts beneath the North American Plate, in Venezuela, lateral movement leads to different outcomes. “It’s a very rare phenomenon, but the probability isn’t zero. It can occur anywhere in the world where there is interaction between tectonic plates,” Sánchez Pulido says. 与墨西哥不同（墨西哥的科科斯板块俯冲到北美板块之下），在委内瑞拉，侧向运动导致了不同的结果。“这是一种非常罕见的现象，但概率并非为零。它可能发生在世界上任何存在构造板块相互作用的地方，”桑切斯·普利多说。

What was surprising was not only that two major earthquakes occurred but that the second struck just 39 seconds after the first. To Sánchez Pulido, that short interval is what made this set of quakes so destructive. 令人惊讶的不仅是发生了两次大地震，而且第二次地震在第一次地震后仅39秒就发生了。对桑切斯·普利多来说，正是这个短暂的间隔使得这组地震具有如此大的破坏性。

“Many structures sustained some kind of damage from the first earthquake. That doesn’t mean the damage was extensive, but any damage alters the original behavior for which they were designed. When another earthquake of similar magnitude strikes immediately afterward, there is no longer any opportunity to reinforce, inspect, or repair the structure. As a result, it no longer performs as intended,” he says. “许多建筑物在第一次地震中受到了一定程度的损坏。这并不意味着损坏很严重，但任何损坏都会改变其设计时的原始性能。当随后立即发生另一次震级相似的地震时，人们再也没有机会去加固、检查或修复结构。结果，它无法再按预期发挥作用，”他说。

That helps explain scenes like the one Eduardo Burger witnessed in Altamira: “The San Miguel building began to crumble,” he recalls. “The walls on the first and second floors broke away and fell right where I was standing.” As he and another person ran toward the center of the street to get to safety, he watched as a building swayed “like a pendulum.” 这有助于解释爱德华多·伯格在阿尔塔米拉目睹的场景：“圣米格尔大楼开始坍塌，”他回忆道。“一楼和二楼的墙壁脱落，正好掉在我站的地方。”当他和另一个人跑向街道中心寻求安全时，他看到一栋建筑像“钟摆”一样摇晃。

The Same Street, Different Damage

同一条街，不同的破坏

Yet not all buildings were affected equally. Sánchez Pulido explains that every building has a natural period of vibration—that is, a frequency at which it tends to oscillate. When that frequency matches part of the energy released by an earthquake, a phenomenon known as resonance occurs, which can significantly amplify the structure’s movement. The engineer compares this to a glass that can shatter when a voice reaches exactly the right frequency. 然而，并非所有建筑物受到的影响都相同。桑切斯·普利多解释说，每栋建筑都有一个固有振动周期，即它倾向于振荡的频率。当该频率与地震释放的部分能量相匹配时，就会发生所谓的“共振”现象，这会显著放大结构的运动。这位工程师将其比作当声音达到特定频率时会破碎的玻璃杯。

“When a building happens to resonate with the earthquake—regardless of its structural strength or whether it was well- or poorly designed—this resonance phenomenon sets in, and then a building that might have moved only slightly due to the earthquake ends up moving much more,” he says. “当建筑物恰好与地震产生共振时——无论其结构强度如何，也无论其设计好坏——这种共振现象就会发生，原本可能因地震仅轻微晃动的建筑，最终会剧烈摇晃，”他说。

Sánchez Pulido emphasizes that quality of construction isn’t the only reason some buildings collapsed while others stayed standing. Another variable is the type of soil on which they were built. 桑切斯·普利多强调，建筑质量并不是导致某些建筑倒塌而另一些保持完好的唯一原因。另一个变量是它们所建造的土壤类型。

Each type of soil—whether rocky, soft, or claylike—alters the way seismic waves reach the surface and, consequently, the response of the buildings. But Venezuelan regulations do not incorporate the level of detail that other countries do, Sánchez Pulido says. 每种类型的土壤——无论是岩石、松软还是粘土——都会改变地震波到达地表的方式，从而影响建筑物的反应。但桑切斯·普利多表示，委内瑞拉的法规并没有像其他国家那样包含如此详细的规定。

“In Mexico City, there are tools developed by the UNAM Institute of Engineering that allow us to determine with great precision how the soil will behave in different areas … When we build our structures, we tailor them specifically to the soil in which they will be built. Unfortunately, upon diving deep into Venezuela’s regulations, I found that they aren’t nearly as specific,” he notes. “在墨西哥城，墨西哥国立自治大学（UNAM）工程研究所开发的工具使我们能够非常精确地确定土壤在不同区域的表现……当我们建造结构时，我们会根据其所在的土壤进行专门定制。遗憾的是，在深入研究委内瑞拉的法规后，我发现它们远没有那么具体，”他指出。

That difference can influence how buildings behave during a high-intensity earthquake, especially when it comes to a phenomenon as unusual as a double earthquake. 这种差异会影响建筑物在高强度地震中的表现，尤其是在面对像双重地震这样罕见的现象时。

To Return or Not to Return: Uncertainty in the Wake of the Earthquake

回还是不回：地震后的不确定性

While experts try to understand what happened, thousands of families are uncertain of whether they’ll be able… 在专家们试图了解发生了什么的同时，成千上万的家庭不确定他们是否能够……