1964年阿拉斯加地震:大阿拉斯加地震

The Setting: Alaska's Subduction Zone

Alaska sits atop one of the world's most seismically active 俯冲带一个构造板块潜入另一板块之下并进入地幔的区域。俯冲带产生世界上最大的地震（8.5级以上），并伴有深海沟和火山弧。 systems. The Pacific Plate subducts beneath the North American Plate along the Aleutian Trench at roughly 6 centimeters per year, making this one of the most productive convergent margins on Earth. Historical records and geological evidence document a long history of great earthquakes along the Aleutian arc, and the rupture zone of the 1964 earthquake — the Alaska-Aleutian 俯冲带一个构造板块潜入另一板块之下并进入地幔的区域。俯冲带产生世界上最大的地震（8.5级以上），并伴有深海沟和火山弧。 — had been identified as a region of high seismic potential. In 1964, Alaska had been a US state for only five years, and much of its infrastructure was relatively new and designed without specific seismic provisions. Anchorage, the largest city with approximately 100,000 people, was built primarily on glacial outwash deposits — a mix of sand, gravel, and silt that was prone to ground failure during strong shaking. The city's newer residential neighborhoods had been developed on Turnagain Heights, an area underlain by particularly sensitive clay deposits.

The Earthquake: March 27, 1964

At 5:36 PM on Good Friday, March 27, 1964, the largest earthquake in US history struck approximately 125 kilometers east of Anchorage, beneath Prince William Sound. 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 M9.2, making it the second most powerful earthquake ever recorded by modern instruments, exceeded only by the 1960 Chile earthquake. The 断层破裂地震期间岩石沿断层发生破裂，将储存的弹性能量以地震波形式释放的过程。破裂长度小到数米（小地震），大到超过1,000公里（大地震）。 extended approximately 800 kilometers from near Kodiak Island to southeast Alaska, with the seafloor rising by up to 9 meters in some areas and subsiding by up to 2 meters in others. Strong shaking lasting 4 to 5 minutes was experienced across an area of over 800,000 square kilometers. 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 was so powerful that 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。 needles went off-scale at stations across North America. In Anchorage, the devastating 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。 of the Bootlegger Cove Clay — a sensitive marine clay deposited after the last ice age — caused catastrophic landslides in the Turnagain Heights neighborhood and downtown Anchorage. Thirty blocks of the central business district dropped 3 to 6 meters as the ground failed around them.

The Science: Documenting Ground Failure

The 1964 Alaska earthquake became one of the most thoroughly studied events in earthquake science history, in part because it occurred in a wealthy country with strong scientific institutions and in part because the scale and variety of ground failures were exceptional. The 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。 of the Bootlegger Cove Clay represented one of the most dramatic and well-documented examples of 侧向扩展液化过程中，土壤块体沿自由面（陡坡或河岸）方向发生水平移动的现象。可对基础设施、桥梁和管线造成广泛破坏。 ever recorded: entire neighborhoods slid toward Cook Inlet as the clay layer beneath them lost its bearing capacity under cyclic loading from 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。 train. 断层破裂地震期间岩石沿断层发生破裂，将储存的弹性能量以地震波形式释放的过程。破裂长度小到数米（小地震），大到超过1,000公里（大地震）。 at the surface was observed along portions of the rupture zone, and geodetic surveys documented the pattern of uplift and subsidence with remarkable precision — valuable data for understanding megathrust earthquake mechanics. The 海啸由水下地震导致海底突然位移而产生的一系列海浪。海啸可以喷气机般的速度（时速700公里以上）穿越整个大洋盆地。 generated by the 1964 earthquake was the most destructive in North American history. Local waves struck the communities of Valdez, Chenega, Whittier, and Seward within minutes, killing dozens and destroying waterfront infrastructure. The regional 海啸由水下地震导致海底突然位移而产生的一系列海浪。海啸可以喷气机般的速度（时速700公里以上）穿越整个大洋盆地。 propagated throughout the Pacific Ocean: waves 4 to 6 meters high struck Crescent City, California, killing 11 people and causing $7.5 million in damage. Waves were measured in Japan, Antarctica, and throughout the Pacific basin. Use the Earthquake Energy Calculator to explore how the energy of this M9.2 event compares to other great earthquakes in American history.

The Impact: Transformation of Alaska

The 1964 Alaska earthquake killed 139 people — a remarkably low toll given its magnitude, reflecting Alaska's sparse population and the good fortune of the 5:36 PM timing (many residents were home rather than in commercial buildings that subsequently collapsed). The economic damage was approximately $311 million in 1964 dollars. The town of Valdez was so severely damaged by 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 海啸由水下地震导致海底突然位移而产生的一系列海浪。海啸可以喷气机般的速度（时速700公里以上）穿越整个大洋盆地。 that it had to be relocated to a more stable site. Seward's waterfront was destroyed, and the railroad terminus burned when oil tanks ignited. The port of Kodiak was devastated. The communities of Chenega on Prince William Sound lost 23 of their 75 residents to the tsunami — 31 percent of the population, one of the highest proportional losses of any community. Across Prince William Sound, the permanent coastal deformation caused by the earthquake dramatically altered the geography: some islands rose more than 10 meters, exposing former seafloor, while other areas dropped below the tidal zone, flooding former forests with seawater.

The Response and Rebuilding

The US federal government, working through the Army Corps of Engineers and the Small Business Administration, provided extensive reconstruction assistance. The rebuilding of Valdez on a new site became a model for how communities can use post-earthquake reconstruction as an opportunity to reduce future risk rather than simply restoring what existed before. Anchorage undertook a systematic program of soil stabilization and foundation retrofitting. The earthquake also prompted a major expansion of the US 地震观测网由若干地震台站协同组成、持续监测地震活动的系统。全球地震台网（GSN）拥有150多个台站，提供全球范围的观测覆盖。 in Alaska and a reassessment of 概率地震危险性分析（PSHA）一种量化地震危险性的方法，综合考虑所有可能的地震震源、震级及地震动水平，以超过特定震动水平的概率来表示结果。 across the Pacific Northwest, where analogous 俯冲带一个构造板块潜入另一板块之下并进入地幔的区域。俯冲带产生世界上最大的地震（8.5级以上），并伴有深海沟和火山弧。 conditions existed along the Cascadia zone.

The Legacy: Warning Systems and Building Codes

The 1964 Alaska earthquake had lasting impacts on both tsunami science and 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。 development in the United States. It demonstrated that 俯冲带一个构造板块潜入另一板块之下并进入地幔的区域。俯冲带产生世界上最大的地震（8.5级以上），并伴有深海沟和火山弧。 earthquakes produce not just local tsunamis but ocean-crossing waves capable of killing people thousands of kilometers away, directly motivating improvements to the Pacific Tsunami Warning System. It revealed that 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。 of sensitive marine clays could be a dominant cause of structural damage even at distances far from 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。, leading to new provisions in foundation engineering practice. The M9.2 event also recalibrated American scientific understanding of what was possible along the Cascadia 俯冲带一个构造板块潜入另一板块之下并进入地幔的区域。俯冲带产生世界上最大的地震（8.5级以上），并伴有深海沟和火山弧。 in the Pacific Northwest, where a comparable fault system had been identified. The recognition that Seattle, Portland, and Vancouver might face a Cascadia earthquake of similar magnitude eventually drove major investments 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。 programs, school safety assessments, and public 地震防灾准备为减轻地震影响而持续进行的规划与准备过程，包括固定家具、制定通讯计划、储备应急物资以及开展演练。 campaigns across the Pacific Northwest.