如何读地震波记录

What Is a Seismogram?

A 地震记录图地震仪记录的输出结果，以时间为函数显示地面运动情况。地震学家通过分析地震记录图来确定地震的震级、深度和位置。 is the continuous written or digital record produced by a 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。 — the device that measures ground motion at a fixed location. Reading a seismogram is fundamental to seismology because all earthquake science ultimately rests on the interpretation of these waveform records. The pattern of wiggles on a seismogram encodes the earthquake's location, depth, magnitude, fault geometry, and the properties of the Earth's interior through which the waves traveled.

The Three Components of Motion

Modern seismographs record ground motion in three orthogonal directions: vertical (Z), north-south (N), and east-west (E). The vertical component is most sensitive to 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。 arrivals and is often used for initial magnitude estimates. The horizontal components are essential for detecting 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。 arrivals and for determining the direction to the source. Analyzing all three components together allows seismologists to measure the full three-dimensional particle motion of the ground.

Understanding the Time Axis

The horizontal axis of a seismogram represents time, typically annotated with UTC timestamps. Modern digital seismograms sample ground motion at 100 or 200 samples per second, providing precise timing. The precision of arrival time measurements is critical — a timing error of even 0.1 seconds can shift hypocenter location estimates by several kilometers. GPS synchronization ensures that all stations in a 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。 share a common time reference, making cross-station arrival time comparisons valid.

Identifying the P-Wave Arrival

The 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。 arrival is the first signal to appear on the seismogram, emerging abruptly from the background noise level (called the noise floor). P-waves are compressional waves that push and pull the ground in the direction of wave propagation, creating a sharp onset that is relatively easy to identify on the vertical component. The amplitude of the P-wave phase is typically smaller than the subsequent S-wave arrival for earthquakes at teleseismic distances, making it recognizable as the first but smaller deflection on the record.

Identifying the S-Wave Arrival

The 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。 arrival appears after the P-wave, with the time gap between them — known as the S-P time — providing a direct measure of the distance to the earthquake. S-waves are shear waves that move the ground perpendicular to the direction of propagation. On the seismogram, the S-wave arrival is typically much larger in amplitude than the P-wave, producing a clearly visible increase in the 波振幅地震波偏离静止位置的最大位移量。振幅与波所携带的能量直接相关，用于震级计算。 of the record. The S-wave arrival is most prominent on horizontal components.

Using the S-P Time to Estimate Distance

The relationship between S-P time and distance is well established. For earthquakes within the crust, each second of S-P time corresponds to approximately 8 kilometers of distance from the station to 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。. A 10-second S-P time indicates approximately 80 km distance. With S-P readings from three or more stations, triangulation yields the epicenter location. This technique, used routinely by seismologists, can be performed manually on printed seismograms or calculated automatically by the Earthquake Energy Calculator tool.

Surface Waves on the Seismogram

After the P- and S-wave arrivals, longer-period oscillations appear on the seismogram: the 面波沿地球表面而非内部传播的地震波。速度慢于体波，但因振幅更大、持续时间更长，通常造成更大破坏。 phases. Love waves arrive first and appear prominently on the horizontal components, moving the ground sideways in a horizontal shearing motion. Rayleigh waves一种使地面以类似海浪的椭圆运动方式运动的面波，以瑞利勋爵命名，通常是地震时感受到的滚动感的成因。 arrive slightly later and produce an elliptical retrograde particle motion visible on both vertical and horizontal components. Surface waves have the largest 波振幅地震波偏离静止位置的最大位移量。振幅与波所携带的能量直接相关，用于震级计算。 on the seismogram for shallow earthquakes and are responsible for most of the felt shaking and structural damage in populated areas.

The Coda: After the Main Phases

Following the principal wave arrivals, the seismogram shows a gradually decaying sequence of scattered energy called the 尾波地震记录图上主要地震波到达之后的尾部部分，由地壳非均质结构对波的散射引起。尾波持续时间与地震震级相关。. Coda waves are S-wave energy scattered from heterogeneities in the crust and pile up in time as multiply scattered paths arrive at the station. The duration of the coda can be used to estimate magnitude — longer, more energetic codas indicate larger earthquakes. Coda duration magnitude was historically used in regional networks before waveform moment tensor analysis became routine.

Distinguishing Earthquakes from Noise

Reading seismograms requires distinguishing genuine seismic signals from cultural noise (traffic, machinery, ocean waves) and instrumental artifacts. Traffic noise appears as nearly continuous low-frequency tremor with regular daily patterns — peaking during commute hours and quiet at night. Ocean microseisms create persistent energy in the 0.1–0.2 Hz band. Instrumental glitches produce sudden spikes or offsets with unrealistic physical characteristics. Genuine earthquake signals have characteristic phase sequences (P then S then surface waves) and coherent appearance across multiple stations in the network.

Digital Seismogram Analysis Tools

Software packages like ObsPy (Python), SAC (Seismic Analysis Code), and SeisComp enable interactive analysis of digital seismograms. These tools support filtering, phase picking, spectrogram computation, and magnitude estimation from waveforms. The IRIS (EarthScope) DMC provides free access to waveform data for any catalogued earthquake through its web services, making professional-grade seismogram analysis accessible to researchers and advanced students. The Earthquake Energy Calculator tool provides simplified magnitude calculations that help contextualize what you observe in waveform data.

Reading Seismograms at Teleseismic Distances

For earthquakes recorded at distances greater than 1,000 km (teleseismic range), the seismogram appearance changes significantly. P-waves have passed through the deep mantle, where higher velocities produce earlier arrivals. Multiple P-wave phases appear, including PP (reflected off the surface once), PPP (reflected twice), and PcP (reflected off the core-mantle boundary). The time separations between these phases encode information about Earth's deep interior structure, and their analysis formed the basis for our understanding of mantle and core composition.

Summary

A 地震记录图地震仪记录的输出结果，以时间为函数显示地面运动情况。地震学家通过分析地震记录图来确定地震的震级、深度和位置。 is a window into both the earthquake source and Earth's interior. By recognizing the characteristic arrival patterns of P-waves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-waves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。, and surface waves沿地球表面而非内部传播的地震波。速度慢于体波，但因振幅更大、持续时间更长，通常造成更大破坏。, understanding the significance of 波振幅地震波偏离静止位置的最大位移量。振幅与波所携带的能量直接相关，用于震级计算。 variations, and knowing how to use S-P times to estimate distance, you gain the ability to extract meaningful seismological information from what might otherwise appear to be a confusing sequence of wiggles. Combined with tools like the Earthquake Energy Calculator, seismogram reading transforms from a specialist skill into an accessible analytical capability.