Misplaced Pages

#192807

66-504: The Pacific Northwest Seismic Network , or PNSN , collects and studies ground motions from about 400 seismometers in the U.S. states of Oregon and Washington . PNSN monitors volcanic and tectonic activity, gives advice and information to the public and policy makers, and works to mitigate earthquake hazard. Damaging earthquakes are well known in the Pacific Northwest , including several larger than magnitude 7, most notably

132-529: A 16 mm film . The machine was developed by Teledyne Geotech during the mid-1960s. It can automatically plot seismograms from 18 seismic signal sources and 3 time signals on a continuous reel of film. The signals from seismometers are processed by 15.5 Hz recording galvanometers which record the seismograms to a reel of 200 feet (61 m) of film at the speeds between 3 and 20 centimetres (1.2 and 7.9 in) per minute. The machine has self-contained circulating chemicals that are used to automatically develop

198-458: A feedback circuit. The amount of force necessary to achieve this is then recorded. In most designs the electronics holds a mass motionless relative to the frame. This device is called a "force balance accelerometer". It measures acceleration instead of velocity of ground movement. Basically, the distance between the mass and some part of the frame is measured very precisely, by a linear variable differential transformer . Some instruments use

264-408: A geo-sismometro , possibly the first use of a similar word to seismometer . Naturalist Nicolo Zupo devised an instrument to detect electrical disturbances and earthquakes at the same time (1784). The first moderately successful device for detecting the time of an earthquake was devised by Ascanio Filomarino in 1796, who improved upon Salsano's pendulum instrument, using a pencil to mark, and using

330-431: A linear variable differential capacitor . That measurement is then amplified by electronic amplifiers attached to parts of an electronic negative feedback loop . One of the amplified currents from the negative feedback loop drives a coil very like a loudspeaker . The result is that the mass stays nearly motionless. Most instruments measure directly the ground motion using the distance sensor. The voltage generated in

396-664: A magnetic field . Seismogram A seismogram is a graph output by a seismograph . It is a record of the ground motion at a measuring station as a function of time. Seismograms typically record motions in three cartesian axes (x, y, and z), with the z axis perpendicular to the Earth's surface and the x- and y- axes parallel to the surface. The energy measured in a seismogram may result from an earthquake or from some other source, such as an explosion . Seismograms can record many things, and record many little waves, called microseisms . These tiny events can be caused by heavy traffic near

462-541: A copy of which can be found at the University Library in Bologna, and a further mercury seismoscope was constructed by Niccolò Cacciatore in 1818. James Lind also built a seismological tool of unknown design or efficacy (known as an earthquake machine) in the late 1790s. Pendulum devices were developing at the same time. Neapolitan naturalist Nicola Cirillo set up a network of pendulum earthquake detectors following

528-406: A digital seismograph can be simply input to a computer. It presents the data in a standard digital format (often "SE2" over Ethernet ). The modern broadband seismograph can record a very broad range of frequencies . It consists of a small "proof mass", confined by electrical forces, driven by sophisticated electronics . As the earth moves, the electronics attempt to hold the mass steady through

594-520: A given quake. Luigi Palmieri , influenced by Mallet's 1848 paper, invented a seismometer in 1856 that could record the time of an earthquake. This device used metallic pendulums which closed an electric circuit with vibration, which then powered an electromagnet to stop a clock. Palmieri seismometers were widely distributed and used for a long time. By 1872, a committee in the United Kingdom led by James Bryce expressed their dissatisfaction with

660-433: A hair attached to the mechanism to inhibit the motion of a clock's balance wheel. This meant that the clock would only start once an earthquake took place, allowing determination of the time of incidence. After an earthquake taking place on October 4, 1834, Luigi Pagani observed that the mercury seismoscope held at Bologna University had completely spilled over, and did not provide useful information. He therefore devised

726-414: A low-budget way to get some of the performance of the closed-loop wide-band geologic seismographs. Strain-beam accelerometers constructed as integrated circuits are too insensitive for geologic seismographs (2002), but are widely used in geophones. Some other sensitive designs measure the current generated by the flow of a non-corrosive ionic fluid through an electret sponge or a conductive fluid through

SECTION 10

#1733086083193

792-540: A portable device that used lead shot to detect the direction of an earthquake, where the lead fell into four bins arranged in a circle, to determine the quadrant of earthquake incidence. He completed the instrument in 1841. In response to a series of earthquakes near Comrie in Scotland in 1839, a committee was formed in the United Kingdom in order to produce better detection devices for earthquakes. The outcome of this

858-482: A seismometer was deployed on the planet Mars by the InSight lander, the first time a seismometer was placed onto the surface of another planet. In Ancient Egypt , Amenhotep, son of Hapu invented a precursor of seismometer, a vertical wooden poles connected with wooden gutters on the central axis functioned to fill water into a vessel until full to detect earthquakes. In AD 132 , Zhang Heng of China's Han dynasty

924-417: A seismometer. For each predefined interval of data, the helicorder will plot the seismic data in one line before moving to the next line at the next interval. The paper must be changed after the helicorder writes on the last line of the paper. In the model that use ink, regular maintenance of the pen must be done for accurate recording. A Develocorder is a machine that records multi-channel seismic data into

990-508: A sense coil on the mass by the magnet directly measures the instantaneous velocity of the ground. The current to the drive coil provides a sensitive, accurate measurement of the force between the mass and frame, thus measuring directly the ground's acceleration (using f=ma where f=force, m=mass, a=acceleration). One of the continuing problems with sensitive vertical seismographs is the buoyancy of their masses. The uneven changes in pressure caused by wind blowing on an open window can easily change

1056-499: A vacuum to reduce disturbances from air currents. Zollner described torsionally suspended horizontal pendulums as early as 1869, but developed them for gravimetry rather than seismometry. Early seismometers had an arrangement of levers on jeweled bearings, to scratch smoked glass or paper. Later, mirrors reflected a light beam to a direct-recording plate or roll of photographic paper. Briefly, some designs returned to mechanical movements to save money. In mid-twentieth-century systems,

1122-574: Is a digital strong-motion seismometer, or accelerograph . The data from such an instrument is essential to understand how an earthquake affects man-made structures, through earthquake engineering . The recordings of such instruments are crucial for the assessment of seismic hazard , through engineering seismology . A strong-motion seismometer measures acceleration. This can be mathematically integrated later to give velocity and position. Strong-motion seismometers are not as sensitive to ground motions as teleseismic instruments but they stay on scale during

1188-432: Is a more efficient way to read a seismogram. Secondly, there are the minute-marks. A minute mark looks like a hyphen "-" between each minute. Minute marks count minutes on seismograms. From left to right, each mark stands for a minute. Each seismic wave looks different. The P wave is the first wave that is bigger than the other waves (the microseisms ). Because P waves are the fastest seismic waves, they will usually be

1254-450: Is called seismometry , a branch of seismology . The concept of measuring the "shaking" of something means that the word "seismograph" might be used in a more general sense. For example, a monitoring station that tracks changes in electromagnetic noise affecting amateur radio waves presents an rf seismograph . And helioseismology studies the "quakes" on the Sun . The first seismometer

1320-499: Is managed by UW staff. Additional funding is provided by the Department of Energy , the State of Washington , and the State of Oregon . Seismometer A simple seismometer, sensitive to up-down motions of the Earth, is like a weight hanging from a spring, both suspended from a frame that moves along with any motion detected. The relative motion between the weight (called the mass) and

1386-502: Is measured, it is usually the vertical because it is less noisy and gives better records of some seismic waves. The foundation of a seismic station is critical. A professional station is sometimes mounted on bedrock . The best mountings may be in deep boreholes, which avoid thermal effects, ground noise and tilting from weather and tides. Other instruments are often mounted in insulated enclosures on small buried piers of unreinforced concrete. Reinforcing rods and aggregates would distort

SECTION 20

#1733086083193

1452-443: Is placed under the arm, and a small sheet of metal mounted on the underside of the arm drags in the oil to damp oscillations. The level of oil, position on the arm, and angle and size of sheet is adjusted until the damping is "critical", that is, almost having oscillation. The hinge is very low friction, often torsion wires, so the only friction is the internal friction of the wire. Small seismographs with low proof masses are placed in

1518-537: Is said to have invented the first seismoscope (by the definition above), which was called Houfeng Didong Yi (translated as, "instrument for measuring the seasonal winds and the movements of the Earth"). The description we have, from the History of the Later Han Dynasty , says that it was a large bronze vessel, about 2 meters in diameter; at eight points around the top were dragon's heads holding bronze balls. When there

1584-512: Is the output of the seismometer, which is recorded digitally. In other systems the weight is allowed to move, and its motion produces an electrical charge in a coil attached to the mass which voltage moves through the magnetic field of a magnet attached to the frame. This design is often used in a geophone , which is used in exploration for oil and gas. Seismic observatories usually have instruments measuring three axes: north-south (y-axis), east–west (x-axis), and vertical (z-axis). If only one axis

1650-575: Is the second largest of the regional seismic networks in the ANSS ( Advanced National Seismic System ) and has produced more data than the networks in the states of Alaska , Utah , Nevada , Hawaii and the New Madrid, Missouri-Tennessee-Kentucky-Arkansas area. The network is funded primarily by the United States Geological Survey , which stations its own staff on the campus, and the network

1716-511: Is thought to refer to a pendulum, though it is not known exactly how this was linked to a mechanism that would open only one dragon's mouth. The first earthquake recorded by this seismoscope was supposedly "somewhere in the east". Days later, a rider from the east reported this earthquake. By the 13th century, seismographic devices existed in the Maragheh observatory (founded 1259) in Persia, though it

1782-439: Is unclear whether these were constructed independently or based on the first seismoscope. French physicist and priest Jean de Hautefeuille described a seismoscope in 1703, which used a bowl filled with mercury which would spill into one of eight receivers equally spaced around the bowl, though there is no evidence that he actually constructed the device. A mercury seismoscope was constructed in 1784 or 1785 by Atanasio Cavalli ,

1848-452: The Greek σεισμός, seismós , a shaking or quake, from the verb σείω, seíō , to shake; and μέτρον, métron , to measure, and was coined by David Milne-Home in 1841, to describe an instrument designed by Scottish physicist James David Forbes . Seismograph is another Greek term from seismós and γράφω, gráphō , to draw. It is often used to mean seismometer , though it is more applicable to

1914-445: The inertia to stay still within the frame . The result is that the stylus scratched a pattern corresponding with the Earth's movement. This type of strong-motion seismometer recorded upon a smoked glass (glass with carbon soot ). While not sensitive enough to detect distant earthquakes, this instrument could indicate the direction of the pressure waves and thus help find the epicenter of a local quake. Such instruments were useful in

1980-423: The 1731 Puglia Earthquake, where the amplitude was detected using a protractor to measure the swinging motion. Benedictine monk Andrea Bina further developed this concept in 1751, having the pendulum create trace marks in sand under the mechanism, providing both magnitude and direction of motion. Neapolitan clockmaker Domenico Salsano produced a similar pendulum which recorded using a paintbrush in 1783, labelling it

2046-726: The M9 1700 Cascadia earthquake and the M7.0–7.3 earthquake in about 900AD on the Seattle Fault . The M6.5 1965 Puget Sound earthquake shook the Seattle, Washington , area, causing substantial damage and seven deaths. This event spurred the installation of the Pacific Northwest Seismic Network in 1969 to monitor regional earthquake activity. Early in 1980 PNSN scientists detected unrest under Mt. St. Helens and by March 1980 predicted an eruption

Pacific Northwest Seismic Network - Misplaced Pages Continue

2112-482: The analysis of the 1906 San Francisco earthquake . Further analysis was performed in the 1980s, using these early recordings, enabling a more precise determination of the initial fault break location in Marin county and its subsequent progression, mostly to the south. Later, professional suites of instruments for the worldwide standard seismographic network had one set of instruments tuned to oscillate at fifteen seconds, and

2178-426: The archives in the early digital recording days are not recoverable. Today, many other forms are used to digitally record the seismograms into digital medias. Seismograms are read from left to right. Time marks show when the earthquake occurred. Time is shown by half-hour (thirty-minute) units. Each rotation of the seismograph drum is thirty minutes. Therefore, on seismograms, each line measures thirty minutes. This

2244-548: The current available seismometers, still using the large 1842 Forbes device located in Comrie Parish Church, and requested a seismometer which was compact, easy to install and easy to read. In 1875 they settled on a large example of the Mallet device, consisting of an array of cylindrical pins of various sizes installed at right angles to each other on a sand bed, where larger earthquakes would knock down larger pins. This device

2310-402: The density of the air in a room enough to cause a vertical seismograph to show spurious signals. Therefore, most professional seismographs are sealed in rigid gas-tight enclosures. For example, this is why a common Streckeisen model has a thick glass base that must be glued to its pier without bubbles in the glue. It might seem logical to make the heavy magnet serve as a mass, but that subjects

2376-451: The device to begin recording, and then a recording surface would produce a graphical illustration of the tremors automatically (a seismogram). However, the instrument was not sensitive enough, and the first seismogram produced by the instrument was in 1887, by which time John Milne had already demonstrated his design in Japan . In 1880, the first horizontal pendulum seismometer was developed by

2442-419: The film. However, the machine takes at least ten minutes from the time of recording to the time that the film can be viewed. After the digital processing had been used, the archives of the seismograms were recorded on magnetic tapes. The data from the magnetic tapes can then be read back to reconstruct the original waveforms. Due to the deterioration of older magnetic tape medias, large number of waveforms from

2508-425: The first horizontal pendulum was used in a seismometer, reported by Milne (though it is unclear if he was the original inventor). After these inventions, Robert Mallet published an 1848 paper where he suggested ideas for seismometer design, suggesting that such a device would need to register time, record amplitudes horizontally and vertically, and ascertain direction. His suggested design was funded, and construction

2574-414: The first modern seismometer. This produced the first effective measurement of horizontal motion. Gray would produce the first reliable method for recording vertical motion, which produced the first effective 3-axis recordings. An early special-purpose seismometer consisted of a large, stationary pendulum , with a stylus on the bottom. As the earth started to move, the heavy mass of the pendulum had

2640-649: The fiscal year commencing October 1, 2018, calls for reductions in funding and staff for the early warning notification program. The network operates from the Earth and Space Sciences Department at the University of Washington in Seattle, and its data archiving is at the Data Management Center of the IRIS Consortium in Seattle. The network is also affiliated with the University of Oregon Department of Geology. It

2706-478: The frame provides a measurement of the vertical ground motion . A rotating drum is attached to the frame and a pen is attached to the weight, thus recording any ground motion in a seismogram . Any movement from the ground moves the frame. The mass tends not to move because of its inertia , and by measuring the movement between the frame and the mass, the motion of the ground can be determined. Early seismometers used optical levers or mechanical linkages to amplify

Pacific Northwest Seismic Network - Misplaced Pages Continue

2772-450: The garden-gate described above. Vertical instruments use some kind of constant-force suspension, such as the LaCoste suspension. The LaCoste suspension uses a zero-length spring to provide a long period (high sensitivity). Some modern instruments use a "triaxial" or "Galperin" design , in which three identical motion sensors are set at the same angle to the vertical but 120 degrees apart on

2838-634: The horizontal. Vertical and horizontal motions can be computed from the outputs of the three sensors. Seismometers unavoidably introduce some distortion into the signals they measure, but professionally designed systems have carefully characterized frequency transforms. Modern sensitivities come in three broad ranges: geophones , 50 to 750 V /m; local geologic seismographs, about 1,500 V/m; and teleseismographs, used for world survey, about 20,000 V/m. Instruments come in three main varieties: short period, long period and broadband. The short and long period measure velocity and are very sensitive, however they 'clip'

2904-498: The light was reflected to a pair of differential electronic photosensors called a photomultiplier. The voltage generated in the photomultiplier was used to drive galvanometers which had a small mirror mounted on the axis. The moving reflected light beam would strike the surface of the turning drum, which was covered with photo-sensitive paper. The expense of developing photo-sensitive paper caused many seismic observatories to switch to ink or thermal-sensitive paper. After World War II,

2970-422: The location and magnitude of earthquakes. Prior to the availability of digital processing of seismic data in the late 1970s, the records were done in a few different forms on different types of media. A Helicorder drum is a device used to record data into photographic paper or in the form of paper and ink. A piece of paper is wrapped around a rotating drum of the helicorder which receives the seismic signal from

3036-476: The next year, one being a common-pendulum seismometer and the other being the first seismometer using a damped horizontal pendulum. The innovative recording system allowed for a continuous record, the first to do so. The first seismogram was recorded on 3 November 1880 on both of Ewing's instruments. Modern seismometers would eventually descend from these designs. Milne has been referred to as the 'Father of modern seismology' and his seismograph design has been called

3102-417: The older instruments in which the measuring and recording of ground motion were combined, than to modern systems, in which these functions are separated. Both types provide a continuous record of ground motion; this record distinguishes them from seismoscopes , which merely indicate that motion has occurred, perhaps with some simple measure of how large it was. The technical discipline concerning such devices

3168-407: The other at ninety seconds, each set measuring in three directions. Amateurs or observatories with limited means tuned their smaller, less sensitive instruments to ten seconds. The basic damped horizontal pendulum seismometer swings like the gate of a fence. A heavy weight is mounted on the point of a long (from 10 cm to several meters) triangle, hinged at its vertical edge. As the ground moves,

3234-442: The pier as the temperature changes. A site is always surveyed for ground noise with a temporary installation before pouring the pier and laying conduit. Originally, European seismographs were placed in a particular area after a destructive earthquake. Today, they are spread to provide appropriate coverage (in the case of weak-motion seismology ) or concentrated in high-risk regions ( strong-motion seismology ). The word derives from

3300-470: The present architecture of the network results in a significant delay in the early warning notification program, depending upon the location of the quake, leading to proposals to again expand the network. The early warning notification program was implemented with its reliability contingent upon unknown future funding, but with the election of Donald Trump "future funding is uncertain" according to Washington Congressman Derek Kilmer . The president's budget for

3366-400: The seismograph to errors when the Earth's magnetic field moves. This is also why seismograph's moving parts are constructed from a material that interacts minimally with magnetic fields. A seismograph is also sensitive to changes in temperature so many instruments are constructed from low expansion materials such as nonmagnetic invar . The hinges on a seismograph are usually patented, and by

SECTION 50

#1733086083193

3432-551: The seismograph, waves hitting a beach, the wind, and any number of other ordinary things that cause some shaking of the seismograph. Historically, seismograms were recorded on paper attached to rotating drums, a kind of chart recorder . Some used pens on ordinary paper, while others used light beams to expose photosensitive paper. Today, practically all seismograms are recorded digitally to make analysis by computer easier. Some drum seismometers are still found, especially when used for public display. Seismograms are essential for finding

3498-475: The seismometers developed by Milne, Ewing and Gray were adapted into the widely used Press-Ewing seismometer . Modern instruments use electronic sensors, amplifiers, and recording devices. Most are broadband covering a wide range of frequencies. Some seismometers can measure motions with frequencies from 500 Hz to 0.00118 Hz (1/500 = 0.002 seconds per cycle, to 1/0.00118 = 850 seconds per cycle). The mechanical suspension for horizontal instruments remains

3564-413: The signal or go off-scale for ground motion that is strong enough to be felt by people. A 24-bit analog-to-digital conversion channel is commonplace. Practical devices are linear to roughly one part per million. Delivered seismometers come with two styles of output: analog and digital. Analog seismographs require analog recording equipment, possibly including an analog-to-digital converter. The output of

3630-438: The small motions involved, recording on soot-covered paper or photographic paper. Modern instruments use electronics. In some systems, the mass is held nearly motionless relative to the frame by an electronic negative feedback loop . The motion of the mass relative to the frame is measured, and the feedback loop applies a magnetic or electrostatic force to keep the mass nearly motionless. The voltage needed to produce this force

3696-435: The strongest seismic shaking. Strong motion sensors are used for intensity meter applications. Accelerographs and geophones are often heavy cylindrical magnets with a spring-mounted coil inside. As the case moves, the coil tends to stay stationary, so the magnetic field cuts the wires, inducing current in the output wires. They receive frequencies from several hundred hertz down to 1 Hz. Some have electronic damping,

3762-643: The team of John Milne , James Alfred Ewing and Thomas Gray , who worked as foreign-government advisors in Japan, from 1880 to 1895. Milne, Ewing and Gray, all having been hired by the Meiji Government in the previous five years to assist Japan's modernization efforts, founded the Seismological Society of Japan in response to an Earthquake that took place on February 22, 1880, at Yokohama (Yokohama earthquake). Two instruments were constructed by Ewing over

3828-455: The time the patent has expired, the design has been improved. The most successful public domain designs use thin foil hinges in a clamp. Another issue is that the transfer function of a seismograph must be accurately characterized, so that its frequency response is known. This is often the crucial difference between professional and amateur instruments. Most are characterized on a variable frequency shaking table. Another type of seismometer

3894-516: The weight stays unmoving, swinging the "gate" on the hinge. The advantage of a horizontal pendulum is that it achieves very low frequencies of oscillation in a compact instrument. The "gate" is slightly tilted, so the weight tends to slowly return to a central position. The pendulum is adjusted (before the damping is installed) to oscillate once per three seconds, or once per thirty seconds. The general-purpose instruments of small stations or amateurs usually oscillate once per ten seconds. A pan of oil

3960-539: Was an earthquake, one of the dragons' mouths would open and drop its ball into a bronze toad at the base, making a sound and supposedly showing the direction of the earthquake. On at least one occasion, probably at the time of a large earthquake in Gansu in AD 143, the seismoscope indicated an earthquake even though one was not felt. The available text says that inside the vessel was a central column that could move along eight tracks; this

4026-420: Was an inverted pendulum seismometer constructed by James David Forbes , first presented in a report by David Milne-Home in 1842, which recorded the measurements of seismic activity through the use of a pencil placed on paper above the pendulum. The designs provided did not prove effective, according to Milne's reports. It was Milne who coined the word seismometer in 1841, to describe this instrument. In 1843,

SECTION 60

#1733086083193

4092-520: Was attempted, but his final design did not fulfill his expectations and suffered from the same problems as the Forbes design, being inaccurate and not self-recording. Karl Kreil constructed a seismometer in Prague between 1848 and 1850, which used a point-suspended rigid cylindrical pendulum covered in paper, drawn upon by a fixed pencil. The cylinder was rotated every 24 hours, providing an approximate time for

4158-423: Was constructed in 'Earthquake House' near Comrie, which can be considered the world's first purpose-built seismological observatory. As of 2013, no earthquake has been large enough to cause any of the cylinders to fall in either the original device or replicas. The first seismographs were invented in the 1870s and 1880s. The first seismograph was produced by Filippo Cecchi in around 1875. A seismoscope would trigger

4224-719: Was expanded to other Cascade Mountains volcanoes. The PNSN, in conjunction with the Cascades Volcano Observatory of the USGS , now monitors seismicity at all the Cascade volcanoes in Washington and Oregon. The network was significantly expanded after the damaging 2001 Nisqually earthquake . After an earthquake on January 30, 2009, the network's emergency notification system failed. A magnitude 4.3 earthquake in February 2015 showed that

4290-431: Was likely to occur "soon". On March 27 the first steam and ash explosion occurred. The PNSN expanded to better monitor Mt. St. Helens and other Cascade Volcanos leading up to the deadly May 18 eruption and in the years following. Earthquakes are recorded frequently beneath Mount St. Helens , Mount Rainier , and Mount Hood . After successfully using seismic activity to predict the 1980 Mt. St. Helens eruption , monitoring

4356-653: Was made in China during the 2nd century. It was invented by Zhang Heng , a Chinese mathematician and astronomer. The first Western description of the device comes from the French physicist and priest Jean de Hautefeuille in 1703. The modern seismometer was developed in the 19th century. Seismometers were placed on the Moon starting in 1969 as part of the Apollo Lunar Surface Experiments Package . In December 2018,

#192807