1989年洛马普里埃塔地震:世界大赛地震

The Setting: The San Francisco Bay Area

The San Andreas Fault runs through the heart of the San Francisco Bay Area, one of the most seismically monitored and studied regions on Earth. In October 1989, the Bay Area was acutely aware of earthquake risk — the memory of the 1906 disaster was embedded in local culture, and seismologists at UC Berkeley and the USGS had been documenting the complex system of Bay Area faults for decades. The Santa Cruz Mountains segment of the San Andreas Fault had not produced a major earthquake since a M6.5 event in 1906 and was identified as a 地震空区与相邻区段相比长时间未发生地震的活动断层区段，可能预示未来发生地震的概率有所增加。 with elevated probability of future rupture. Urban development across the Bay Area had produced a highly variable building stock: modern reinforced concrete and steel frame buildings in the new commercial districts; older 软层（薄弱层）通常因车库或商铺等大开口而导致强度明显弱于上部楼层的建筑楼层（通常为首层）。软层是最常见的建筑倒塌机制。 apartment buildings with open parking garages at ground level; Victorian wood-frame houses; and the Nimitz Freeway (Interstate 880) double-deck highway elevated on columns through the residential neighborhoods of West Oakland, an area underlain by deep bay mud deposits highly susceptible to 场地放大效应（土壤放大）软弱土壤或沉积层放大地震波而引起的震动强度增大现象。建在软土上的建筑物所承受的震动强度可达基岩上建筑物的2至10倍。.

The Earthquake: October 17, 1989

At 5:04 PM on October 17, 1989 — Game 3 of the World Series between the San Francisco Giants and Oakland Athletics was about to begin at Candlestick Park — the Santa Cruz Mountains segment of the San Andreas Fault ruptured beneath Loma Prieta peak. The 震级量化地震所释放总能量的单一数值。震级每增加一个整数单位，释放的能量约增加31.6倍。 was M6.9. The 震源地震破裂在地球内部实际发生的位置，也称焦点。震源深度对地表感受到的震动方式有重大影响。 was approximately 18 kilometers deep, and the 震中地震发生在地下的震源正上方对应的地表位置，新闻报道中通常将其作为地震发生的位置。 was roughly 95 kilometers south of San Francisco. Though the magnitude was not exceptional, the earthquake occurred on a 走滑断层岩石块沿水平方向相互滑动错开的断层。圣安德烈亚斯断层和北安纳托利亚断层是引发破坏性地震的主要走滑断层。 with an oblique reverse component, the rupture was relatively shallow, and the 地震波由地震或爆炸产生并在地球内部传播的弹性波。地震波将震源释放的能量传送到远处地点。 energy traveled efficiently through the Bay Area's basement rock to the deep sediment basins beneath Oakland and the Marina District of San Francisco, where 场地放大效应（土壤放大）软弱土壤或沉积层放大地震波而引起的震动强度增大现象。建在软土上的建筑物所承受的震动强度可达基岩上建筑物的2至10倍。 dramatically increased ground motion. The earthquake lasted approximately 15 seconds — brief enough that most Bay Area residents experienced it as a sharp violent jolt rather than the extended rolling motion of a distant great earthquake.

The Science: Amplification and the Soft-Story Failure

The Loma Prieta earthquake provided one of the most dramatic and well-documented examples of 场地放大效应（土壤放大）软弱土壤或沉积层放大地震波而引起的震动强度增大现象。建在软土上的建筑物所承受的震动强度可达基岩上建筑物的2至10倍。 in earthquake history. The areas of greatest damage were not near the 震中地震发生在地下的震源正上方对应的地表位置，新闻报道中通常将其作为地震发生的位置。 in the Santa Cruz Mountains but were concentrated in areas more than 100 kilometers away underlain by soft bay mud and artificial fill — the Nimitz Freeway corridor in Oakland and the Marina District of San Francisco. Strong-motion 地震仪用于探测并记录地震波引起的地面运动的仪器。现代数字地震仪可探测到小于一纳米的位移。 recordings showed that ground acceleration on soft soil in Oakland exceeded bedrock values by a factor of three to five. The Nimitz Freeway (Interstate 880), built on deep bay mud through West Oakland, suffered catastrophic collapse of its upper deck over a 2-kilometer stretch, killing 42 people and demonstrating the lethal potential of 结构共振当地震波频率与建筑物固有频率相匹配时发生的建筑物运动放大现象。低层建筑易与高频波产生共振，高层建筑则易与低频波产生共振。 between the dominant 波周期地震波相邻两个波峰之间的时间间隔。长周期波（10—20秒）传播距离更远，用于面波震级的计算。 of soft-soil ground motion and the natural frequency of the elevated roadway structure. 液化饱和松散土壤在强烈震动下暂时失去强度、表现如液体般的现象。可导致建筑物下沉、倾斜或陷入地下坍塌。 extensively damaged the Marina District, an area of San Francisco built on sand and rubble fill from the 1906 earthquake reconstruction. 软层（薄弱层）通常因车库或商铺等大开口而导致强度明显弱于上部楼层的建筑楼层（通常为首层）。软层是最常见的建筑倒塌机制。 failures — the same mechanism that would devastate Kobe six years later — killed occupants in multiple Bay Area apartment buildings, particularly in the unreinforced lower-floor open parking configurations prevalent in buildings constructed between the 1960s and early 1980s. Use the Distance from Epicenter tool to understand how ground motion varied across the Bay Area based on distance and soil conditions.

The Impact: 63 Dead, Billions Lost

The Loma Prieta earthquake killed 63 people — a remarkably low toll compared to events of similar magnitude in less-prepared regions, but a number that carried enormous weight because it exposed specific, addressable vulnerabilities in the world's most earthquake-aware major metropolitan area. Three distinct collapse events accounted for the majority of deaths: 42 on the Nimitz Freeway, 6 in the collapse of a section of the Bay Bridge upper deck, and the remainder in building collapses in Santa Cruz and the Marina District. Total economic losses were approximately $6 billion. The Bay Bridge, which carries approximately 250,000 vehicles per day, was closed for a month for repairs, severely disrupting the regional economy. San Francisco's Marina District — ironically, one of the city's wealthiest neighborhoods — suffered extensive damage because of its 液化饱和松散土壤在强烈震动下暂时失去强度、表现如液体般的现象。可导致建筑物下沉、倾斜或陷入地下坍塌。-prone fill substrate, demonstrating that 场地放大效应（土壤放大）软弱土壤或沉积层放大地震波而引起的震动强度增大现象。建在软土上的建筑物所承受的震动强度可达基岩上建筑物的2至10倍。 hazard does not correlate with economic status.

The Response and Policy Reform

The “你感觉到了吗？”（DYFI）美国地质调查局的一项计划，收集震后公众的烈度报告，形成基于公众参与的烈度分布图，任何感受到地震的人都可以提交报告。 reporting system was used extensively in the aftermath, with over 11,000 observations submitted to the USGS. The 震度速报图（ShakeMap）美国地质调查局在地震发生后发布的成果，展示地面震动强度的分布情况，综合了地震仪数据、地震动模型以及“你感觉到了吗？”的报告。 concept — developed in part from the lessons of Loma Prieta — was refined after this event to better represent the systematic effect of local soil conditions on ground motion. The earthquake triggered two major policy reforms in California: the Seismic Hazards Mapping Act, which required cities to identify 液化饱和松散土壤在强烈震动下暂时失去强度、表现如液体般的现象。可导致建筑物下沉、倾斜或陷入地下坍塌。 and landslide zones and disclose them to property buyers; and expanded mandatory 抗震加固对既有建筑进行强化以提高其抗震能力的工程措施，常见方法包括增设钢支撑、加固基础以及将结构与基础用螺栓连接。 programs for 软层（薄弱层）通常因车库或商铺等大开口而导致强度明显弱于上部楼层的建筑楼层（通常为首层）。软层是最常见的建筑倒塌机制。 buildings and 无筋砌体未配置钢筋加固的砖石或砌块结构，对地震震动极为脆弱。无筋砌体建筑是全球地震死亡人数中占比最高的建筑类型。 structures, eventually leading to the comprehensive mandatory retrofit ordinances adopted by San Francisco and Los Angeles.

The Legacy: The World Series Earthquake

The Loma Prieta earthquake earned its popular name — the World Series Earthquake — from the remarkable coincidence of striking during a nationally televised baseball game, meaning that millions of Americans watched the initial chaos unfold live on ABC Sports. This unprecedented media exposure made the earthquake one of the most culturally prominent seismic events in American history and helped build public support for earthquake preparedness investment. Scientifically, Loma Prieta contributed foundational data on 场地放大效应（土壤放大）软弱土壤或沉积层放大地震波而引起的震动强度增大现象。建在软土上的建筑物所承受的震动强度可达基岩上建筑物的2至10倍。, 液化饱和松散土壤在强烈震动下暂时失去强度、表现如液体般的现象。可导致建筑物下沉、倾斜或陷入地下坍塌。, and 软层（薄弱层）通常因车库或商铺等大开口而导致强度明显弱于上部楼层的建筑楼层（通常为首层）。软层是最常见的建筑倒塌机制。 collapse that directly influenced subsequent 抗震建筑规范为确保建筑物达到最低地震安全水平而制定的一套法律要求，涉及建筑的设计与施工，通常在重大地震暴露出新的薄弱环节后进行修订。 revisions across California and the western United States. The Nimitz Freeway collapse became an iconic symbol of infrastructure vulnerability to earthquake hazard, motivating billions of dollars in 抗震加固对既有建筑进行强化以提高其抗震能力的工程措施，常见方法包括增设钢支撑、加固基础以及将结构与基础用螺栓连接。 investment in California's highway and bridge system that directly saved lives in subsequent earthquakes.