震中(epicenter) vs 震源(hypocenter):有什么区别?

Epicenter: The Point on the Surface

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。 is the point on the Earth's surface directly above where an earthquake begins. It is the location reported in news headlines — "earthquake strikes 30 km south of city X" — because it tells you where on the map the seismic energy originated most directly above ground. The epicenter is the geographically relevant location for emergency responders, residents, and infrastructure managers trying to understand where they should focus their attention.

However, it is crucial to understand that the epicenter is a projected point on the surface, not where the rupture actually started. The actual rupture initiation point is always somewhere below the surface. For a shallow earthquake 10 km deep, the epicenter is a reasonable proxy for the source location. For a deep earthquake 200 km below the surface, the epicenter might be more than 100 km away from the closest surface expression of the fault system, and the area of maximum surface shaking may not even be centred on the epicenter.

Hypocenter: Where the Rupture Begins

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。 (also called the focus) is the three-dimensional point within the Earth where the earthquake rupture initiates. It is defined by three coordinates: latitude, longitude, and depth. The depth is often the most uncertain of the three, because determining depth requires particularly good data coverage — ideally stations both near the epicenter and at varying distances.

Understanding the hypocenter depth is essential for hazard assessment. Shallow earthquakes (less than 70 km deep) release their energy closer to the surface and generally cause more intense surface shaking for a given magnitude than deep earthquakes. The 2015 Nepal earthquake (Mw 7.8) had a hypocenter approximately 15 km deep, which contributed to its devastating surface shaking. By contrast, deep focus earthquakes in the 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。s beneath South America and the Kuril Islands occur at depths exceeding 500–600 km; although some of these events have very large magnitudes, their great depth means the shaking at the surface is spread over a much larger area and is less intense locally.

How Scientists Triangulate Earthquake Locations

Locating an earthquake requires solving for four unknowns: latitude, longitude, depth, and time of origin. The data used are the arrival times of P波（纵波）速度最快的地震波，能以每秒5至8公里的速度穿过固体岩石和液体。P波沿传播方向压缩和拉伸介质，形似弹簧振动，是最先到达地震观测站的波。s and S波（横波）使岩石垂直于传播方向运动的地震波，晚于P波到达。S波无法穿过液体，这一特性证明了地球外核为液态。s at 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。 stations of known location. With the travel time from a station and knowledge of wave velocities in the Earth, a circle of possible hypocenter locations can be drawn around each station. With three stations, the three circles intersect at (ideally) one point that gives the epicenter. With four or more stations, over-determined systems allow both epicenter and depth to be estimated simultaneously.

In practice, Earth's velocity structure is not perfectly known, stations have timing uncertainties, and seismic waves are affected by complex three-dimensional geology. Modern earthquake location algorithms use iterative least-squares fitting to minimise the mismatch between observed and predicted arrival times, often incorporating three-dimensional velocity models and waveform cross-correlation to achieve sub-kilometre location accuracy for well-recorded events. The 全球地震台网（GSN）由150多个宽频带地震台站组成的全球网络，提供对全球地震活动的全面监测，由美国地质调查局、美国国家科学基金会及IRIS联合运营。's global station coverage has made it possible to reliably locate earthquakes anywhere on Earth to within a few tens of kilometres under routine operating conditions.

Why Depth Matters: Shallow vs Deep Earthquakes

Earthquake depth profoundly influences the distribution and character of surface shaking. Consider two earthquakes, both of magnitude 7.0: one at 10 km depth and one at 200 km depth. The shallow earthquake concentrates its energy in a small area directly above the hypocenter, producing intense, potentially devastating shaking in a limited region. The deep earthquake spreads its energy over a much larger footprint at the surface, producing moderate shaking over a wide area — potentially felt across an entire country — but with less intensity at any individual location.

Depth also affects what types of secondary hazards are produced. Shallow earthquakes are more likely to generate 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。s (if they occur under the ocean and involve significant vertical displacement of the seafloor), 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 saturated soils, and permanent 地表破裂地震期间沿断层在地表产生的可见位移。跨越地表破裂带建造的构筑物，无论结构强度如何都可能被撕裂破坏。 visible at the surface. Very deep earthquakes rarely generate tsunamis because the seafloor deformation, transmitted through hundreds of kilometres of rock, is diffuse rather than concentrated. The geographic footprint of a deep earthquake is so large that even with a high 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。, the local 地震烈度根据对人员、建筑物和自然环境的观测影响，衡量特定地点震动强度的指标，随距震中距离增大而降低。 at 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。 may be surprisingly modest.

The Role of Seismic Networks in Location Accuracy

The accuracy of hypocenter and epicenter determinations has improved dramatically over the past century, driven by the growth of 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。s from a handful of stations to global networks of thousands. The 全球地震台网（GSN）由150多个宽频带地震台站组成的全球网络，提供对全球地震活动的全面监测，由美国地质调查局、美国国家科学基金会及IRIS联合运营。, operated by the 美国地质调查局（USGS）负责监测地震、运营国家地震信息中心并向全球发布实时地震数据的美国政府主要机构。 and partner institutions, provides high-quality broadband data from more than 150 stations worldwide, enabling reliable location of earthquakes above about magnitude 4.0 anywhere on Earth.

Regional dense networks — like those operated by CalTech in Southern California, the Japan Meteorological Agency, and seismological institutes in New Zealand and Switzerland — provide vastly denser station coverage within their regions, enabling location accuracies of a kilometre or less for local events. This precision is essential for aftershock studies, fault mapping, and verifying compliance with nuclear test ban treaties. Use the Distance from Epicenter tool to estimate how far you are from an earthquake's epicentre and how that distance affects the shaking you might experience.