GPS与地震:测量地面变形

GPS Geodesy and Plate Motion Measurement

Before the Global Positioning System (GPS) was available for scientific geodesy, measuring the slow movement of 构造板块地球岩石圈中不断移动、漂浮、有时发生断裂的巨大板块。共有7个主要板块和约8个次要板块，它们之间的相互作用引发了绝大多数地震。s required decades of precise surveying using optical instruments, with accuracies limited to millimeters at best over short distances. GPS transformed the field. Modern continuous GPS receivers at fixed monuments can measure horizontal positions to sub-millimeter precision and vertical positions to a few millimeters, recording data every second, every day, year after year. By analyzing the accumulated displacement of GPS monuments over years to decades, scientists can directly measure 构造板块地球岩石圈中不断移动、漂浮、有时发生断裂的巨大板块。共有7个主要板块和约8个次要板块，它们之间的相互作用引发了绝大多数地震。 velocities with remarkable accuracy — and detect the subtle deformation that precedes, accompanies, and follows earthquakes.

The GNSS Revolution

While "GPS" remains the common term, modern geodetic networks actually use signals from multiple Global Navigation Satellite System (GNSS) constellations: US GPS, Russian GLONASS, European Galileo, and Chinese BeiDou. Using multiple constellations improves positioning geometry, accuracy, and reliability. Dense GNSS networks like the Southern California Integrated GPS Network (SCIGN), the Pacific Northwest Geodetic Array (PANGA), and Japan's GEONET (over 1,300 stations) provide a continuous, high-resolution picture of surface deformation across entire tectonic regions.

Continuous GPS Networks Along Faults

Continuous GPS networks along active 断层线断层在地表的痕迹，表现为一条线状或破碎岩石带。地质学家绘制活动断层线图，以评估周边社区的地震危险性。s are among the most powerful tools for understanding where seismic strain is accumulating and how fast. Along the San Andreas 断层（地质学）岩石沿其发生位移的破裂面。断层长度从数毫米到数千公里不等。会引发地震的主要断层称为活动断层。 system in California, GPS monuments on either side of the fault move apart at rates of 20–35 millimeters per year — directly measuring the 滑动速率断层沿线位移的平均速率，通常以每年若干毫米衡量。滑动速率越高，通常意味着地震发生频率和危险性越高。 of the fault system. Where a fault is locked因摩擦阻止运动而导致应力持续积累的断层区段。闭锁断层一旦最终破裂，可能引发大地震。, the GPS stations on either side of the fault converge (for a compressional fault) or diverge (for an extensional fault) slowly, building up the elastic strain that will eventually be released in an earthquake. Where a fault is creeping, the GPS stations move smoothly and continuously without the build-up of large locked-zone strain.

Interseismic, Coseismic, and Postseismic Deformation

Geodesists divide the deformation signal around a 断层（地质学）岩石沿其发生位移的破裂面。断层长度从数毫米到数千公里不等。会引发地震的主要断层称为活动断层。 into three phases. Interseismic deformation is the slow build-up of elastic strain as the locked 断层（地质学）岩石沿其发生位移的破裂面。断层长度从数毫米到数千公里不等。会引发地震的主要断层称为活动断层。 accumulates stress between earthquakes — GPS stations show steady, gradual motion that reflects both plate motion and the locking of the fault. Coseismic deformation is the sudden displacement that occurs during the earthquake itself — GPS receivers near the fault may jump by meters within seconds, with the displacement direction and pattern directly reflecting the sense of slip on the fault. Postseismic deformation continues for months to years after the earthquake as viscoelastic relaxation in the lower crust and mantle gradually redistributes the earthquake-induced stress, and as afterslip continues on the deeper part of the 断层（地质学）岩石沿其发生位移的破裂面。断层长度从数毫米到数千公里不等。会引发地震的主要断层称为活动断层。.

Detecting Slow Slip Events

One of the most scientifically significant discoveries of the GPS era in geophysics is the existence of slow slip events (SSEs) — transient episodes of 断层（地质学）岩石沿其发生位移的破裂面。断层长度从数毫米到数千公里不等。会引发地震的主要断层称为活动断层。 slip that release stress without producing significant seismic shaking. First detected in the late 1990s in the Cascadia Subduction Zone using GPS, SSEs appear as brief (days to weeks) reversals in the normally steady interseismic movement of GPS monuments. The Cascadia events occur at intervals of 12–18 months and release stress equivalent to Mw 6.5–6.8 earthquakes on the deeper portion of the subduction interface, just downdip of the locked megathrust zone因摩擦阻止运动而导致应力持续积累的断层区段。闭锁断层一旦最终破裂，可能引发大地震。. Similar slow slip events have been detected in Japan, New Zealand, and Central America. Understanding the relationship between slow slip on the downdip portion of a 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。 and the potential for megathrust rupture on the updip locked zone is one of the central research questions in modern earthquake science.

Co-seismic and Post-seismic Deformation

Large earthquakes produce dramatic co-seismic displacements that are precisely measured by GPS大地测量利用全球定位系统接收机以毫米级精度测量构造板块运动和地壳变形的方法，可揭示地震之间断层上应变积累的过程。. The 2011 Tohoku earthquake (Mw 9.0) moved GPS stations on eastern Honshu up to 5.3 meters eastward and 0.5 meters downward — measurements that directly constrained the distribution of slip on the subduction interface and revealed that slip at the trench was much larger than models had anticipated. The 2010 Maule earthquake (Mw 8.8) in Chile moved coastal stations up to 3 meters horizontally. These co-seismic displacement fields, combined with seismic waveform inversion and 干涉合成孔径雷达（InSAR）通过对比地震前后拍摄的雷达图像，以厘米级精度测量地表形变的卫星雷达技术，可揭示断层的滑动模式。 data, allow the detailed mapping of slip distribution on the fault — which patches slipped most, which remained locked, and what stress changes resulted for surrounding segments.

Afterslip and Viscoelastic Relaxation

In the months and years following a major earthquake, GPS networks detect continued deformation as the crust and mantle adjust to the sudden redistribution of stress. Afterslip — continued fault motion at depths below or adjacent to the main rupture — accounts for some of this post-seismic signal. Viscoelastic relaxation — the slow flow of the ductile lower crust and upper mantle in response to the earthquake-induced stress change — accounts for the rest. Distinguishing these two mechanisms from GPS time series requires sophisticated modeling that incorporates the rheological properties of the crust and mantle. Understanding post-seismic deformation is important for assessing how the stress on neighboring 断层（地质学）岩石沿其发生位移的破裂面。断层长度从数毫米到数千公里不等。会引发地震的主要断层称为活动断层。 segments has changed following a major earthquake, directly informing 库仑应力传递地震改变邻近断层应力状态、从而可能触发或延迟未来地震的过程，用于预测哪些断层正被推向更接近破裂的状态。 transfer calculations.

GPS in Earthquake Early Warning

The same GPS networks that measure long-term tectonic deformation can contribute to 地震预警（EEW）一种在强震到达前探测地震并向人员和系统发送警报的系统，可提供数秒至数十秒的预警时间，足以采取自我保护行动。 systems for large earthquakes. Traditional seismic 地震预警（EEW）一种在强震到达前探测地震并向人员和系统发送警报的系统，可提供数秒至数十秒的预警时间，足以采取自我保护行动。 relies on P-wave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。 detection, which suffers from magnitude saturation for the very largest events — the earthquakes most important to warn about. High-rate GPS (1–10 samples per second) can detect the large static displacements of major earthquakes within seconds of rupture initiation, providing magnitude estimates that do not saturate at high magnitudes. This GPS-based magnitude estimation is particularly important for 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。 megathrust earthquakes like the 2011 Tohoku event, where early seismic estimates were significantly too low. Integration of high-rate GPS大地测量利用全球定位系统接收机以毫米级精度测量构造板块运动和地壳变形的方法，可揭示地震之间断层上应变积累的过程。 data into real-time earthquake monitoring and 地震警报系统墨西哥的SASMEX系统，是世界上最早投入使用的公共地震预警系统之一，自1991年起运行，可为墨西哥城提供长达60秒的沿海地震预警时间。 pipelines is an active area of development at geodetic and seismological agencies worldwide.

Strain Budgets and Seismic Hazard Implications

GPS geodesy has enabled the computation of geodetic strain budgets — quantitative estimates of how fast strain is accumulating on specific faults compared to how fast it is being released through seismic slip. On the Himalayan frontal thrust, GPS measurements show the Indian subcontinent converging with Asia at roughly 20 mm/yr, yet the rate of strain release in large earthquakes falls far short of the geodetically measured convergence rate, implying a large ongoing deficit. These strain budget analyses directly feed into probabilistic seismic hazard assessments by providing independent constraints on long-term fault slip rates, complementing the geological 古地震学通过断层探槽、隆起阶地和海啸沉积物等地质证据研究史前地震的学科，将地震记录延伸至数千年前。 evidence from trenching studies and 断层崖地震期间断层沿垂直方向发生位移而形成的陡崖或陡坡。断层崖可高达数米，是过去地震活动留下的可见证据。 mapping. Where geodetically measured strain rates are high and earthquake recurrence intervals特定断层上相邻两次大地震之间的平均时间间隔，通过古地震学研究和历史记录估算得出。卡斯凯迪亚俯冲带的重现间隔约为500年。 are long, the 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。 concept can be applied to identify segments most likely to host future large earthquakes.