Teach you how to observe the earthquake

Teach you how to observe the earthquake

First, observe the basic aspects of the earthquake ?

First, there must be a sensor to observe the ground motion. This sensor is in close contact with the ground. When the ground vibrates, this sensor converts the ground vibration into the corresponding electrical signal as the output of the sensor. To monitor the earthquake

The sensor used is called a "seismometer." In addition to ground vibrations caused by the propagation of seismic waves to the ground, there are other types of vibration sources, such as waves, storms, vehicles, and various human activities, which can cause ground vibration.

Therefore, not only in the event of an earthquake, but also in the ground, the ground is always vibrating, so the seismometer always outputs electrical signals that reflect ground vibration. The usual ground vibrations have some influence on the observation of seismic signals. We use this kind of ground vibration.

It is called "ground motion noise." In some places, due to the high ground motion noise on the ground, which affects the sensitivity of seismic monitoring, the seismometer is placed in wells several hundred meters deep or even deeper. Such a seismometer is called a downhole seismograph. Ground motion noise

With depth attenuation, the downhole seismometer can record weaker seismic signals better than the ground seismometers in the same place. ?
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Next is a signal transmission device for transmitting the output of the "signal adjustment device" to the recording device. Sometimes, the signal transmission device can be just a cable. Used to connect the output of the signal conditioner to the input of the recorder

. This is the case on many people's seismic stations today. At this time, seismographs and recording devices are collectively referred to as "seismographs." But sometimes, there is a large distance between the signal adjusting device and the recording device.

Within tens of kilometers, even hundreds of kilometers or more. At this time, appropriate signal transmission equipment is needed for transmitting seismic signals through communication links such as wired channels (eg, telephone lines) and wireless channels (eg, ultra-short wave radio stations, artificial satellites).

In the past, this is the so-called seismic telemetry system. For example, a telemetered seismic network includes several stations. Each station has a sender for seismometers, signal conditioning devices, and signal transmission equipment. At the network center, there is a signal transmission and transmission system.

The receiving end of the equipment and the recording device connected thereto. ?

The output signal of the seismometer needs to undergo certain processing. The device for processing the seismometer output signal may be referred to as a "signal adjustment device." It may amplify, digitize, filter, etc. the output signal of the seismometer so that the output signal

The number is more suitable for recording and use.
Recording devices come in many forms. Since the emergence of modern seismometers in the late 19th century, a recording device that has been used up to now is a "drum type" recorder. The transducer on the recorder converts the received electrical signal into the deflection of the beam (using the camera

Paper recording) or pen tip oscillation (ink recording, thermal paper recording, or fume recording). The record drawings thus obtained are what people commonly call "seismograms." ?

The above-mentioned electrical signals reflecting the ground motion and the geodynamic recording curves on the seismograms are continuous, which are called "analogue" signals and "simulation record seismograms". Using the simulated record seismograms, many earthquakes have been obtained

And the internal structure of the Earth. For example, the internal layered structure of the Earth, that is, the Earth has crust, mantle and core from the outside to the inside, the core is divided into the outer core and the core, and the average thickness of each layer is through the analysis of the simulated record seismogram.

Reading data from the seismic record waveforms is calculated. However, there are many deficiencies in the simulated seismic observation system, which limits the acquisition of seismic information, and it is inconvenient to perform more analysis on simulated seismic maps.

. With the development and popularization of modern information technology, digital seismic observations have gradually replaced analog seismic observation systems and become the mainstream of seismic observation. ?

Second, why earthquake observation?

Since earthquakes occur in the depths of a few kilometers, dozens of kilometers, or even hundreds of kilometers underground, and we cannot know the exact time and place of the earthquake before an earthquake occurs, we cannot directly observe the earthquake source.

It can only observe the ground motion caused by the earthquake-induced seismic wave propagating to the ground. By recording the ground motion, it can invert information about the source, such as the time, place, depth and size of the earthquake.

Usually expressed in magnitude). It's like listening to people tapping a bell with your eyes closed. If your ears are sound, then you can not only know when someone knocks on the sound, but also estimate the intensity of the knock and determine the direction of the clock.

. But for the author of this article, the situation is different, because one ear's hearing is close to zero, relying on only one ear, even if I hear the sound, I do not know where the sound comes from. Based on similar reasons, observations of ground motion caused by seismic waves

Many seismic observation instruments (called seismometers) need to be placed in different locations (called seismic stations).

For humans, earthquakes are both a natural disaster that can bring about disasters and a powerful tool for human understanding of the internal structure and evolution of the Earth. As a natural disaster, people need to understand the laws of gestation, occurrence, and development of earthquakes.

And the effects caused by the earthquake, in order to take corresponding predictions and preventive measures, so as to minimize the disaster caused by the earthquake; as human beings to understand the internal structure and evolution of the Earth, we must try to make full use of the earthquake that occurred when the earthquake occurred.

Waves carry information about the source and the Earth's media. Therefore, whether it is to reduce the earthquake disaster or to use the earthquake as a light to instantaneously illuminate the interior of the earth to understand the earth, we must first make observations. This is what we usually do.

The so-called "earthquake observations." ?

This observation of ground motion caused by earthquake-induced seismic waves is a traditional observation of seismicity, commonly known as “seismology,” and more general-purpose seismic observations also include the purpose of earthquake prediction and prediction. Earthquakes

Observations of related phenomena are called “earthquake precursor observations” and the main purpose of their observations is to catch the precursors before the major earthquake. The contents of earthquake precursory observations are extensive. Some of these observations were originally based on a basic view of the geophysical field.

Measurements, such as observations of the geomagnetic field, observations of gravity fields, observations of large terrain variations, etc. Therefore, the earthquake precursory observations mentioned in the earthquake industry essentially include many geophysical fields and other physical quantities that can be used for earth science research.

The amount of scientific observations, according to the general classification method of the earthquake sector, earthquake precursor observations include electromagnetic observations, topography variable observations and underground fluid observations. ?

For the sake of illustration, the following sections are all about traditional seismic observations, ie observations of ground vibrations caused by seismic waves. Earthquake precursor observations will be introduced on other occasions. ?

Third, the characteristics and advantages of digital seismic observation?

The external difference between the digital seismic observation system and the simulated seismic observation system is that the digital seismic observation system records the digital numbers. These digital numbers are stored in the computer's memory (memory and hard disk) and can be transferred to floppy disks, optical disks, etc.

Or tape, can be printed out by the printer, the corresponding curve can be displayed on the screen, it can also be converted into analog, forming a record curve similar to the traditional seismogram. Before running the digital seismic observation system,

Seismic waveforms recorded on seismic maps were computer processed and artificial waveforms were used to digitize seismic waveform records. The basic approach is to take points (called "sampling") at regular intervals on the recording curve, for example, every 0.5 seconds.

Take a point, then use a ruler to measure the offset of the point relative to the average baseline (called "quantization"). Due to the limitation of the scale of the scale and the resolution of the manually read data, the effective number of digits of the read data is limited, and the numerical value and the actual offset value are limited.

The difference between them is called "quantization error." Now that you have a digital seismic observation system, the analog electrical signal output by the seismometer is “sampled” by the analog-to-digital converter in the data collector (a special signal conditioning device).

"Quantization", then the data collector outputs the digital numbers encoded in binary bits, which are collected in a computer and stored on a computer hard disk, and then stored in other computer-readable media, such as a floppy disk or an optical disk.

Research staff further analysis. ?

The use of digital seismic observation systems to obtain digital seismic waveform data has brought great benefits to earthquake monitoring, rapid earthquake reporting, seismic and geophysical scientific research. ?

First, due to the introduction of a digitalization system and the use of new seismometers, it is possible to obtain wide-band, large-dynamic-range seismic-wave records to obtain richer, more complete, and more realistic information about seismic sources and seismic media.

. The so-called "broad band" refers to geodynamic signals capable of recording from a few tens of Hz (for example, 40 Hz) to a period of several hundred seconds (for example, 360 seconds) even to direct current: the so-called "large dynamic range" that allows the same system to be used from Micro-shock to particularly large

Earthquake signals can record complete seismic waveforms. Compared with the small signal, this large signal can differ by 6 to 7 orders, that is, the amplitude of the large signal can reach more than 1 million times of the small signal amplitude. However, the previous analog recording system can only achieve

To 2 to 3 orders of magnitude. In this way, if an analog observation system is adjusted to be sensitive and small earthquake events can be recorded, then the waveform of a large earthquake event occurring in the same place may be “limited”, that is, a signal exceeding a certain amplitude.

Shaving results in waveform distortion. Conversely, if the analog seismic monitoring system is adjusted to waveforms suitable for recording large earthquake events, the system will be insensitive and small earthquake events will not be recorded. Digital seismic observation system overcomes this

One problem. ?

Second, because the digital seismic observation system records the seismic waveform in a computer, it is easy to use a computer for processing. Through automatic processing and human-computer interaction processing, data can be quickly read from seismic records for source location and earthquake

Determination of size. In this way, after a major earthquake occurs, the epicentral location (latitude and longitude of the epicenter), the depth of the source, the time of the earthquake and the magnitude can be quickly determined. This was a valuable time for earthquake relief and earthquake relief

between. ?

Third, since digital seismic records contain richer information about seismic sources and earth media, and seismic records are easily handled by computers, digital seismic records are particularly suitable for seismic sources and internal structures of the Earth.

Research. For example, in the past, the magnitude of an earthquake was described using traditional magnitudes. When the magnitude of an earthquake is too large, the magnitude of the traditional magnitude (such as the so-called Richter scale) obtained from seismic records is not as great as the so-called magnitude “saturation”. phenomenon

. Using digital seismic records for analysis and processing to obtain the so-called “moment magnitude” can describe the size of the earthquake more accurately. For example, in the famous 1960 Chilean earthquake, the so-called Richter scale magnitude was 8.5 and the “Moment magnitude” was used.

"The grade obtained is 9.2. Using the analysis of digital seismic records, we can clearly infer the rupture process that occurred at the earthquake source at the moment of the major earthquake.

In short, digital seismic observation is a concrete manifestation of the world in the digital era in the field of seismic monitoring, so it can be said that the trend of the world.