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Module 1: Introduction to Seismic Data and Acquisition
模块 1:地震数据和采集简介

Associate Professor Stuart Clark

Term 2, 2024 第 2 学期,2024 年
Week 1 in MERE2002/5002/6002
MERE2002/5002/6002 第 1 周
# Course Materials developed by Stuart Clark and Artur Shapoval, UNSW Sydney
# (c) 2021
# Updated 2022, 2023, 2024 by S. Clark
# import the ability to display HTML and youtube
from IPython.display import HTML, YouTubeVideo
At the end of this module, you should be able to:
  • Understand the different types of seismic waves
  • Be able to calculate reflection coefficients
  • Explain Fermat and Huygen's Principles
  • Describe the acquisition of reflection seismic data in 1D
  • Explain how reflection and refraction seismology differ
  • Plot 1D seismic data using python
    使用 python 绘制一维地震数据

Seismic Waves 地震波

Origin of Terms 术语的起源

earthquakes (Landro and Amundsen, 2018). The first known seismic instrument originates from China and was invented by Chang Heng in AD 132. Called a seismoscope, this instrument was used to detect not only earthquake activity but the direction to the earthquake source. (Dewey and Byerly, 1969) Click here for more information about the device.
地震(Landro 和 Amundsen,2018 年)。已知的第一台地震仪器源自中国,由张衡于公元 132 年发明。这种仪器被称为地震仪,不仅用于探测地震活动,还用于探测震源方向。(杜威和拜尔利,1969 年)点击此处了解有关该仪器的更多信息。
A model of the first seismoscope. This instrument was two meters in diameter with metal balls balanced in each of the dragons' mouths. Strong seismic tremors caused a ball to be released from the mouth of a dragon into the mouth of a frog below, sounding an alarm. The position of the ball falling indicated the direction of the shock wave. (Landro et al., 2018)
第一台地震仪的模型。这个仪器直径两米,每个龙嘴里都有一个金属球。强烈的地震震波会使一个球从龙嘴里释放到下面青蛙的嘴里,从而发出警报。球下落的位置表明了冲击波的方向。(Landro 等人,2018 年)

Portable seismic detectors were first introduced early 1900 s.
便携式地震探测器最早出现在 20 世纪初。

Ludger Mintrop invented a portable seismograph that was deployed to detect salt domes. The device recorded the vertical motion of a ball suspented in a metal cone by spring by a light beam reflected back to the detector unit (in the picture, left):
Ludger Mintrop 发明了一种用于探测盐穹的便携式地震仪。该装置通过反射回探测装置的光束记录被弹簧悬挂在金属锥体中的小球的垂直运动(如左图):
Ludger Mintrop's seismic detector with two parts. A recording device mounted on a tripod that sends a light beam to a mirror in a sensor. The sensor has a mirror attached to a ball and records the movement of the sensor (via the ground) relate to the ball.
Ludger Mintrop 的地震探测器由两部分组成。一个安装在三脚架上的记录装置,将光束发送到传感器中的一面镜子上。传感器上的镜子连接着一个球,记录传感器(通过地面)与球相关的运动。

Types of Waves 波浪类型

(Textbook: p. 17-19) (教科书:第 17-19 页)
P-waves otherwise known as primary (hence ) or compressional waves, move by particles oscillating in the direction the wave travels. In the image below, the colour represents the displacement of the particles to the right (yellow positive, blue negative).
P 波又称原生波(因此称为 )或压缩波,是由沿波行进方向摆动的粒子产生的。在下图中,颜色代表粒子向右的位移(黄色 为正,蓝色 为负)。

S Waves S 波

S-waves known as secondary (hence ) or shear waves, move by particles oscillating perpendicular to the direction the wave travels.
S 波被称为次级波(因此 )或剪切波,是由垂直于波的传播方向的粒子振荡产生的。
Textbook: p. 18 教科书:第 18 页

Wave Propagation 波的传播

Waves propagate in 3 dimensions, spreading out in a spherical shape. We track the amplitudes as they progress outwards by wave fronts. We often also think of the wave moving between two points in a ray. If we can track the ray path between the source of a seismic wave and when we pick it up at a receiver, work out the time that that took , then we know something about the distance travelled and can calculate the velocities that the wave travelled through, since:
波在三维空间中传播,呈球形扩散。我们通过波阵面追踪波幅向外传播的过程。我们通常还认为波在两点之间以射线形式传播。如果我们能够追踪地震波从震源到接收器接收到地震波之间的射线路径,计算出地震波在 所花的时间,那么我们就可以知道 所走的距离,并可以计算出地震波所经过的速度
(Textbook: p. 19) (教科书第 19 页)

Seismic Reflection 地震反射

Waves reflect off interfaces (think of light partially reflected off a smooth pool of water). In the image below, some of the incident wave is reflected back and some continues on . The amount reflected depends on the difference in the seismic impedance between the top layer and the bottom layer . We call this the reflectivity :
波会在界面上发生反射(想想光会在光滑的水池上发生部分反射)。在下图中,入射波 的一部分被反射回 ,另一部分继续传播 。反射量取决于顶层 和底层 之间的地震阻抗差异。我们称之为反射率
. The amplitude of the transmitted wave is calculated in a similar way:
.传输波 的振幅也是通过类似方法计算得出的:
The textbook includes a list of typical reflection coefficients, with good subsurface reflectors having reflectivity - 0.3. A strong near-surface reflector (such as the hard-ocean bottom mentioned) has a reflection coefficient of . What does this mean for the amount of signal transmitted in into the rocks below? Only about one-third of the energy will get through, making the deeper structures harder to see in such a setting.
教科书中列出了典型的反射系数,良好的地表下反射体的反射系数为 - 0.3。强近表层反射体(如提到的硬质洋底)的反射系数为 。这对传输到下面岩石中的信号量意味着什么?只有大约三分之一的能量可以通过,因此在这种情况下,更深层的结构更难被看到。

Seismic Instruments 地震仪器

Here we look at a what a typical seismic acquisition on land comprises.
A vibroseismic truck hits the ground with a series of timed pulses.
This type of seismic acquisition is called active seismic. When the source of sound is uncontrolled - for example, an earthquake, the acquisition is called passive seismic.
Seismic receivers, or geophones, are arranged above the area of interest. Modern geophones are wireless and store their information locally until they are collected and the information downloaded.
The geophones pick up vibrations first directly from the truck and then later from a series of reflections of the energy from the subsurface. The geophones record the time to the layer and up again - called two-way travel time.
Here we are dealing with reflection seismic - the most common type of seismic data used in exploration activities. Refraction seismic data is another type of data that looks at travel times between the source and receiver along layers.

Land Seismic Sensors 陆地地震传感器

A geophone will measure the amount of movement in a direction between a magnet and a coil. The magnet will generate an electric current proportional to the amplitude of the movement in a particular direction.
In the image below, the movement between the ground (which pushed the magnet) and the coil is vertical:
These come in vertical and horizontal variants looking at waves travelling up/down (reflections) and those travelling along layers (refraction). The vertical geophone looks like this:
这些地震检波器分为垂直和水平两种,分别检 测上下传播的波(反射波)和沿层传播的波(折射波)。垂直地震检波器看起来像这样:
The horizontal has the magnet/coil perpendicular to the stake to measure horizontal motions and looks like:

3 Channel Wireless Seismic
3 通道无线地震仪

3 channel sensors have three spikes to measure horizontal (in 2 directions) and vertical displacements. In this case, this is also a wireless unit with a large battery that keeps the geophone recording for long periods ( 1 month).
三通道传感器有三个尖头,用于测量水平(两个方向)和垂直位移。在这种情况下,这也是一个带有大容量电池的无线装置,可以长时间(1 个月)保持地震检波器的记录。
A three channel seismic sensor that can determine direction of wave travel as well as type of wave (c) SmartSolo
三通道地震传感器,可确定波的传播方向和波的类型 (c) SmartSolo

Marine Seismic Acquisition

Marine seismic is acquired via hydrophones (not geophones), usually connected together in long buoyant tubes called streamers. You can see the black hydrophones in the orange streamers in the image below:
海洋地震是通过水听器(而非检波器)采集的,这些水听器通常连接在称为 "流线 "的长浮力管中。您可以在下图中看到橙色流线中的黑色水听器:

Hydrophones 水听器

This cable is a marine cable (orange) with hydrophones (black/silver) at regular intervals
These streamers are laid out by the seismic vessel in long lines behind the vessel. Floats, buoys and paravanes keep the streams going in the correct direction behind the seismic vessel.
In addition, a series of airguns are trailed close to the ship and used as seismic sources. The airguns create waves of energy that move downwards, penetrate the subsurface and eventually bounce back to be received at the many receives located on the streamers. These streamers are also trailed behind the ship - usually several kilometres long and contain multiple receivers listening for reflected seismic waves. Data collected along the streamers are called in-line and those perpendicular to the streamers (and direction of travel of the boat) are called cross-line (or X-line).
此外,一系列气枪被拖曳到船只附近,用作地震源。气枪产生的能量波向下运动,穿透地下,最终反弹到位于幡上的许多接收器上。这些流线也拖在船后,通常有几公里长,包含多个接收器,用于监听反射的地震波。沿幡线收集的数据称为同线数据,垂直于幡线(和船的行进方向)的数据称为横线(或 X 线)数据。
In the example below, there are 10 streamers (each with multiple receivers) and 2 source arrays of 3 air-guns each.
在下面的示例中,有 10 个流媒体(每个流媒体有多个接收器)和 2 个源阵列,每个源阵列有 3 个气枪。
Each of the In-lines represents one of the cables above. Floats and buoys keep the cables in the right positions. A source array of 2 sources is towed ahead of the cables in a traditional layout
每条内线代表上面的一条缆线。浮筒和浮标使电缆保持在正确的位置。由 2 个信号源组成的信号源阵列以传统布局拖曳在电缆前方

Marine Source 海洋资源

You can see what an airgun source, used in marine surveys, looks below:
(Source: Haavik, K., 2016. Source-Depth Diversity for Enhanced Marine Seismic Imaging.)
(资料来源:Haavik, K., 2016:Haavik, K., 2016.用于增强海洋地震成像的源深多样性》(Source-Depth Diversity for Enhanced Marine Seismic Imaging.)

Displaying 1D Seismic Data in Python
用 Python 显示一维地震数据

First, let us consider the following theoretical case displayed in the image below. We have a truck that both operates as a seismic source and receiver. Since the source receiver are at the same location, this is known as zero-offset. The truck sends seismic signals into the Earth below and then listens for reflected waves coming back from the horizons below (these horizons are all horizontal fortunately, otherwise they would bounce the wave away from our truck, not back to it).
This truck records the following data:
at 4 ms intervals. In python, that looks like:
间隔为 4 毫秒。在 python 中,这看起来像


Plotting Seismic Data as a Wiggle

Seismic amplitudes are recorded by the receives as deflections of incoming waves. The longer the wave takes to arrive, generally speaking, the deeper the layer. As such, we display these wiggles as two-way time in the -axis to indicate depth. A wiggle trace represents amplitudes as a continuous line varying about 0 . For more information about displaying seismic data, see the AAPG wiki.
地震振幅是接收器记录的入射波的偏转。一般来说,波到达的时间越长,地层就越深。因此,我们在 - 轴上以双向时间显示这些摇摆来表示深度。摆动轨迹将振幅表示为一条围绕 0 变化的连续线。有关地震数据显示的更多信息,请参阅 AAPG 维基百科。
Since the time for the wave to arrive back is for it to bounce on a particular horizon and come back, we call the time two-way time
The seismic wiggle trace can be plotted using the code below:
# Plot seismic trace
import matplotlib.pyplot as plt # Import our plotting function
# Setup an array to represent the timings of data point on our seismic array
times = np.linspace(0.0,3.6,num=10)
# Create a blank figure and axes
fig, ax = plt.subplots()
# Plotting the data
# Setup axes labels
ax.set(xlabel="Amplitude",ylabel="Two-Way Time (ms)",title="Seismic Wiggle Plot")
ax.invert_yaxis() # plot from top to bottom because the deepest reflections take the lo
# Labelling the horizons
plt.axhline(y = 1.2, linestyle='--', linewidth='0.5', color='grey')#horizontal line at y
plt.text (s = 'Horizon 1', x = -2.5, y = 1.1, c = 'grey') #text at y = 11 so it
plt.axhline(y = 2.4, linestyle='--', linewidth='0.5', color='grey')
plt.text (s = 'Horizon 2', x = 2, y = 2.3, c = 'grey')
plt.axhline(y = 3.6, linestyle='--', linewidth='0.5', color='grey')
plt.text (s = 'Horizon 3', x = -2.5, y = 3.5, c = 'grey');
Seismic Wiggle Plot 地震摇摆图

Variable Density Display

An alternative to the wiggle is the variable density display. These are typically images in which the colour density is used to display the amplitude. In the image below, black and white represent high positive or negative aimplitudes respectively, while middle grays represent low amplitudes.
In this scenario, we will first interpolate the data so that our time recording is instead of ( higher resolution!)
在这种情况下,我们将首先对数据进行插值处理,使我们的时间记录为 ,而不是 ( ,分辨率更高!)
# Create the new time array recorded at 0.01 ms
times_x40 = np.linspace(0,3.6,num=400) # note 400 points not 10
# Interpolate the data
new_seis = np.interp(times_x40,times,seismic_trace)
# Plot ID seismic trace as a Variable Density Display
fig, ax = plt.subplots(1,2)
fig.suptitle("Variable Density Plot (2 colour scales)")
# Transpose the array to plot it vertically - also need to make it 2d for image show (im
new_seis_t = np.transpose(np.atleast_2d(new_seis))
# Left hand image, grey scale
im1 = ax[0].imshow(new_seis_t, cmap = 'gray_r', extent = [0,0.5,3.6,0]) # Plot image
ax[0].set(xlabel=None,xticks=[],ylabel="Two-Way Time (ms)",title="grayscale") #Set axis
fig.colorbar(im1,ax=ax[0], location='bottom',label="Seismic amplitude") # Add colorbar
# Right hand image, seismic colours
im2 = ax[1].imshow(new_seis_t, cmap = 'seismic', extent = [0,0.5,3.6,0])
ax[0].set(xlabel=None,xticks=[],ylabel="Two-Way Time (ms)",title="seismic")
fig.colorbar(im2,ax=ax[1], location='bottom',label="Seismic amplitude")

Seismic Acquisition Keywords

  • Reflection vs transmitted wave
  • P-wave vs S-Wave P 波与 S 波
  • Incident / Reflected Wave
  • Reflection coefficient 反射系数
  • Ray path 射线路径
  • Wave front 波前
  • Verticle geophone 垂直检波器
  • Source array 来源阵列
  • Airgun 气枪
  • Streamer 流线型
  • Seismic Amplitude 地震振幅
  • Variable density plot 变密度图
  • Wiggle plot 扭动情节

References 参考资料

  • Dewey, J., Byerly, P., 1969. The early history of seismometry (to 1900). Bulletin of the Seismological Society of America 59, 183-227. https://doi.org/10.1785/BSSA0590010183
    Dewey, J., Byerly, P., 1969.The early history of seismometry (to 1900).Bulletin of the Seismological Society of America 59, 183-227. https://doi.org/10.1785/BSSA0590010183
  • (Textbook) Gadallah, Mamdouh R. (2009). Seismic Fundamentals (Chapter 3). In Exploration Geophysics, Springer, Berlin, Heidelberg. 9783540851608
    (教科书)Gadallah,Mamdouh R.(2009 年)。地震基础(第 3 章)。In Exploration Geophysics, Springer, Berlin, Heidelberg.9783540851608
  • Landro, M., Amundsen, L., 2018. Introduction to exploration geophysics with recent advances. Bivrost Geo.
    Landro, M., Amundsen, L., 2018.勘探地球物理学导论与最新进展》。Bivrost Geo.
  • Onajite, Enwenode. Seismic Data Analysis Techniques in Hydrocarbon Exploration. Elsevier, 2014. https://doi.org/10.1016/C2013-0-09969-0.
    Onajite, Enwenode.油气勘探中的地震数据分析技术》。Elsevier, 2014. https://doi.org/10.1016/C2013-0-09969-0.