How do you translate a seismogram into plain language or another language without claiming that every wiggle is an earthquake? Read the time axis, the station and channel metadata, the recorded quantity and the arrival sequence before writing about the event. A seismogram is an instrument record of ground motion or a related seismic measurement. It can contain the arrivals of different wave types, local vibration, processing effects and noise. A faithful description must separate what the trace visibly shows from what seismic analysis concludes.
Students searching for how to read a seismogram, identify P-waves and S-waves, explain earthquake waveforms or translate seismic graphs often need help with three distinctions. A wave’s arrival time is not the earthquake’s origin time. The trace’s displayed height is not a direct earthquake-magnitude label. A large-looking line does not establish how much shaking was felt elsewhere. This guide teaches those distinctions through clear explanations, examples and verification routines.
The examples here are schematic and hypothetical unless linked to an official educational source. Earthquake bulletins, safety alerts and hazard assessments should come from competent monitoring authorities. Translation can help people understand a seismic record; it must not pretend to replace validated event processing or public safety guidance.
What a seismogram records and what it does not
A seismometer senses motion associated with ground vibration; a seismograph system records and displays data produced by that sensing arrangement. The resulting seismogram is often drawn as a trace against time. Depending on the instrument, processing and display, the plotted value can relate to displacement, velocity, acceleration or an instrument-specific signal. Translators should preserve the channel’s label instead of calling every vertical excursion ‘distance moved’. The chart is a measurement record at a particular location and with a particular configuration, not a video of the earthquake spreading across the world.
A trace can register earthquakes, but also local vehicles, footsteps near a sensor, wind-related motion, cultural noise, equipment artefacts and other sources. That does not make it meaningless; it means interpretation relies on context. If the document labels a candidate seismic event, distinguish that annotation from the raw squiggle. A careful translation says ‘the waveform contains a signal interpreted by the monitoring report as an earthquake arrival’ when that is what the original supports. It does not infer an epicentre, magnitude or source type from a screenshot alone.
Station, time and channel come before the wiggles
The header often carries a network code, station identifier, geographic location, channel designation, acquisition time and sampling context. These details determine how to interpret the waveform. A record from one station is not a direct map of all motion in a region. A channel that records vertical motion is not interchangeable with a horizontal component, and component orientation can matter greatly. Preserve the station identifier exactly; a transposed letter may point readers to the wrong site or data set.
Check whether timestamps are displayed in Coordinated Universal Time, local civil time or seconds relative to a selected origin. Date boundaries and daylight-saving conventions can shift what a reader thinks happened. If a trace begins at 23:58 and continues past midnight, a translation must preserve the change of date. If the source gives only relative seconds, do not invent a calendar date. Timing is structural scientific data, and an otherwise fluent paragraph can become factually wrong because it silently changes the clock.
Horizontal time is not always the same as event duration
The horizontal axis commonly advances in seconds or minutes, and some web displays compress hours or days into a narrow image. Reading the tick interval matters. A waveform that occupies three centimetres on the page could represent thirty seconds or thirty minutes. Translate actual values, not graphical width. If a viewer zooms into one short time window, that clip no longer describes the whole event. A faithful caption identifies the visible start and end times or notes that the crop omits them.
Earthquake origin time, the moment the source process begins according to a seismic event model, is different from when a wave arrives at a particular receiver. The physical waves travel through Earth before reaching the sensor. Translating ‘arrival at station’ as ‘time the earthquake happened’ collapses that travel interval. When an earthquake report provides an origin time, preserve it as a modelled event parameter. When the screenshot only shows station arrival times, explain precisely that these are observation coordinates on the station’s record.
P-waves: the earliest common seismic arrival
Primary or P-waves are compressional body waves that often travel faster than other major seismic wave types through the materials relevant to introductory earthquake analysis. They commonly produce the first identifiable arrival in a seismogram from an earthquake. But a clear onset is not guaranteed on every channel or at every distance. The translator should not label the first visible wiggle as P without evidence that it is the P arrival. Monitoring analysts use multiple channels, timing, waveforms and travel-time knowledge to make picks.
If the source marks a P-wave arrival at a specific time, retain both the letter and the time. A beginner-friendly explanation can add that it is the first selected seismic arrival in that record. Avoid treating ‘primary’ as meaning ‘most damaging’ or ‘strongest’; the label refers to its place in wave classification and typical arrival sequence. Source terminology matters because the next part of a problem may compare P and S arrival times, and an inaccurate translated label would make the subsequent reasoning impossible.
S-waves: the later shear-wave arrival
Secondary or S-waves are shear body waves, and their propagation behaviour differs from P-waves. In introductory local-earthquake examples, an S arrival typically appears after a P arrival. Its appearance can be marked by a change in waveform character and often larger motion on suitable components, but magnitude of the visual trace alone does not certify the wave type. Translate an identified S arrival only when the source marks it or analysis supports it. ‘Secondary’ does not mean scientifically unimportant.
P and S labels are particularly easy to swap when an image is cropped or the lines are crowded. Confirm which timestamp belongs to which marker rather than inferring from a coloured arrow. If the report gives a reading with uncertainty, preserve that uncertainty. An S-wave pick may be more difficult to identify clearly in noisy data. A target text that replaces ‘possible S arrival’ with ‘S-wave began exactly here’ would erase the analyst’s stated limits and misrepresent the evidence.
Why the S–P interval matters
The time between selected S- and P-wave arrivals provides useful information related to distance from the earthquake source because the two body-wave types generally travel at different speeds. In basic teaching activities, students measure S arrival minus P arrival and compare that interval with a model or travel-time curve. The interval is measured in units of time, often seconds; it is not itself a distance. Translators must preserve whether a number names an arrival time, a time difference or a distance estimate.
A simplistic rule that multiplies S–P seconds by a memorised constant may work only within a specific educational model. Real travel-time relationships depend on wave speeds, Earth structure, source depth, path and selected phases. Good translation preserves the model being applied and its approximation language. Say ‘the S–P time difference is 12 seconds in this hypothetical trace’ before any model-dependent distance calculation. If no model is supplied, the descriptive claim should stop at the measured interval.
Surface waves and later parts of a record
After the initial body-wave arrivals, a seismogram may show later arrivals including surface waves and scattered or reflected energy. The dominant phases depend on source, distance, instrument and frequency range. A novice may call every late large wiggle an S-wave or regard the entire remaining signal as one phase. A faithful translation should use the source’s labels and describe later energy without over-classifying it. ‘Large-amplitude motion follows the initial picked arrivals’ can be accurate without naming a specific wave.
Surface waves can be significant in earthquake shaking, but the display scale and instrument response still govern what is visible. Distinguish a physical wave’s motion from the trace’s screen amplitude. Some wave trains overlap in time. A diagram intended for early science education may simplify the record to three named arrival regions. That simplification is useful if marked as schematic. Translating it as though it were a definitive phase catalogue for every earthquake overstates what the teaching picture is designed to convey.
Amplitude is not earthquake magnitude
Amplitude on a seismogram is a property of the recorded signal as displayed or measured under stated conditions. Earthquake magnitude is an event parameter estimated from appropriate observations using a defined magnitude scale and methodology. A trace from a nearby small event can look visually larger than a trace of a more distant larger event depending on distance, gain, sensor type and processing. Calling a taller line ‘a higher-magnitude earthquake’ based on the image alone is an interpretation error, not merely awkward English.
Magnitude and intensity also differ. Magnitude characterises an event on a scale, while intensity concerns observed effects or shaking at a location under a specified intensity system. One earthquake has a reported magnitude estimate but can produce different intensities across places. Translate these terms consistently. Do not turn a station’s amplitude into a description of damage, and do not turn a public intensity report into a number on the seismogram’s vertical axis. That separation is essential when science information reaches a general audience.
Instrument gain, scaling and the illusion of size
Many waveform displays automatically scale the vertical axis to fit the available screen height. One day’s quiet background noise can fill the same height as a stronger signal displayed at a different gain. If the chart’s range changes, comparing apparent peak heights by eye becomes unreliable. A translator should state a numeric vertical measurement only if the units and scale support it. ‘The display shows a pronounced change in the trace’ is safer than ‘the ground moved one metre’ when the vertical scale is missing.
Some screenshots stack many short segments, each shifted vertically to create a continuous view known as a helicorder or webicorder display. The line wrapping from one row to the next is a presentation device, not a physical jump. The time progression must be reconstructed from labels on each row. Translators unfamiliar with this display can accidentally describe adjacent rows as simultaneous measurements or treat the row boundary as another seismic arrival. State the display type and how its time axis unfolds before narrating an event.
Clipping, saturation and missing samples
A waveform may be clipped when the recorded signal exceeds the instrument or data representation’s usable range. Flat-topped traces can be a sign of saturation, but unusual shapes can also have other causes. The translated description should not treat a clipped value as a valid measurement of the true peak amplitude. If the original marks clipped data, preserve that warning. A quantity measured outside an instrument’s range is not made more accurate by adding decimals to the printed number.
Missing samples, telemetry interruptions and sudden steps can resemble physical events. An apparent gap does not prove the ground stopped moving. Monitoring systems distinguish acquisition quality from geophysical interpretation. Translation needs the same discipline: a note marked ‘data gap’ should remain a data gap, not become an interval of seismic quiet. Quality flags, processing notes and channel availability often seem peripheral, but they prevent readers from making claims the instrument record cannot support.
Filtering and frequency content change the appearance
Signal processing can emphasise or suppress frequency ranges, remove trends and smooth particular kinds of noise. A filtered trace may look different from a raw recording even when it represents the same underlying episode. The translator should retain labels such as band-pass, high-pass, low-pass or processed where present. The difference is not optional terminology: a waveform feature visible after filtering may be less obvious in an unprocessed record, and the numerical amplitudes may not be directly comparable.
Frequency and amplitude are different properties. Rapidly oscillating lines indicate shorter periods or higher frequencies relative to the selected scale, while larger vertical excursions indicate a bigger signal value in the plotted unit. A common explanation failure calls faster oscillations ‘stronger shaking’. A careful caption can describe both separately: ‘The oscillations become more closely spaced, and the recorded amplitude also changes.’ Translation must preserve the relationship actually shown rather than treating all visually busy motion as one generic intensification.
Three-component records need three separate descriptions
Seismic stations often provide recordings from vertical and two horizontal components. The channels can have different orientations and sensitivities, and a component’s label may carry this information. When translating an image with three traces, identify which is which before comparing arrivals. A wave may be prominent on one component and less distinct on another. Do not combine separate channels into a single invented trace. A good prose account says which features appear on which labelled line.
Orientation abbreviations such as Z, N and E may refer to components, but the exact naming convention should be verified against the source station metadata. If the figure uses rotated radial and transverse components, those are not simply synonyms for north and east. Technical translation should retain unfamiliar but meaningful labels, adding brief definitions when reliable. Simplifying away the channel distinction might seem reader-friendly, yet it erases precisely the information needed for correct seismic interpretation.
One station does not uniquely locate an earthquake
A single station and an S–P time difference can constrain source distance under a suitable travel-time model, but distance alone generally does not identify one unique point on a map. Introductory lessons often combine estimates from multiple stations to narrow down location. A translator must not turn ‘the source is about a certain distance from Station A’ into ‘the epicentre is at Station A’. Nor should they replace a reported uncertainty region with an exact street-level location. The distinction between observation and location solution is fundamental.
Earthquake epicentre refers to the surface position above the focus or hypocentre, while the hypocentre describes the source location at depth in a simplified earthquake model. Translators should retain the terms separately. A map, travel-time inversion and additional observations are needed to establish a location estimate according to the monitoring method. A screenshot of one waveform rarely carries that full chain. When the task is simply to explain P and S arrivals, avoid importing a confident location story from general earthquake knowledge.
Magnitude scales and the risks of familiar names
Public discussions sometimes treat Richter magnitude, moment magnitude and other scales as if they were interchangeable labels for any earthquake number. Operational bulletins use defined scales for particular methods. A translator should reproduce the scale designation the source gives, if any, rather than replacing it with the most familiar name. Numerical precision and uncertainty also matter. A reported magnitude is an estimate that can be revised as further data become available.
Do not use descriptive adjectives such as catastrophic, harmless or severe as automatic translations of a magnitude value. Effects depend on depth, distance, ground conditions, structures and other factors. When a source document explicitly describes impacts, translate those observations as impacts. When it only reports magnitude, do not invent consequences. This is especially important in rapidly changing news and public information, where confident but unsupported language may mislead people about their local risk.
Reading an official event annotation
Some seismogram screenshots include event labels, phase picks, analyst notes, network origin estimates or automated alerts. These annotations represent interpretations or data products, not necessarily things visible from the waveform alone. Translation can preserve them faithfully while making their source explicit: ‘the bulletin identifies the event as…’ differs from ‘the trace visibly proves…’. If an event solution is marked preliminary, the target must retain that status. If a phase is marked tentative, keep the qualification.
Automated and reviewed event products can differ. A monitoring network may update location, depth or magnitude after more stations report. When translating archived charts, record which report version or issue time the figure represents. The purpose is not to undermine reliable science but to respect scientific process. A careful reader is better served by a source-attributed estimate with limits than a target sentence that sounds certain because the translator omitted the original qualification.
Language traps: onset, arrival, peak, period and duration
‘Onset’ can mean the beginning of a selected signal; ‘arrival’ refers to when a wave phase reaches the receiver; ‘peak amplitude’ concerns an extreme signal value; ‘period’ concerns one oscillation’s timescale; ‘duration’ concerns how long an interval lasts. In everyday speech these may be collapsed into ‘when it happened’ or ‘how big it was’. A technical translator keeps them apart. The correct target equivalent must express the physical role rather than just resemble the source word.
Build a small glossary with definitions tied to the figure. Under ‘P arrival’, write ‘the selected time at which the P-phase is interpreted to reach the sensor.’ Under ‘S–P interval’, write ‘later S pick minus earlier P pick’. Under ‘magnitude’, write ‘an event estimate made using a specified scale’. Test the glossary by explaining a new trace without looking at the original English labels. Cross-language fluency is useful only when it protects those distinct concepts.
How to create an accessible verbal description
Begin with the station and channel if known, then the time window, horizontal scale and plotted vertical quantity. State whether the figure shows one waveform or multiple components. Describe the main changes in signal character, identifying annotated P and S arrivals and their times when supplied. Then distinguish late arrivals, uncertainty marks and noise. End with a statement about what the plot alone cannot establish. This order lets readers reconstruct the important relations without sight of the graph.
A screen-reader-friendly caption might say: ‘The displayed station waveform runs from 12:00 to 12:02 UTC. An analyst marker identifies a P arrival at 12:00:24 and an S arrival at 12:00:37. A larger-amplitude wave train follows. The figure does not show a magnitude calculation.’ This is both concise and cautious. If the image includes three components, label each separately; do not rely on red, green and blue as their sole identifiers.
Cross-language verification of times, symbols and place names
Clock notation can shift between 12-hour and 24-hour formats, and local dates can differ from UTC dates. The translation needs a rule for time-zone conversion and a record of whether any conversion was actually made. Names of seismic stations, network codes, channels, event IDs and phase labels should normally be preserved as controlled identifiers. Transliterate location names only according to a consistent reference and retain a traceable original where useful.
Numeric checks should cover arrival timestamps, S–P differences, units, decimal punctuation, signs and any interval endpoints. A slip of one minute changes an inferred travel-time measurement dramatically. A typo in a station code may direct a reader to another instrument. Scientific translation quality assurance is therefore part language review and part structured data comparison. Read the target independently for clarity, then compare every critical string against the original record.
Learning to explain rather than merely label
Early learners may memorise that P arrives first and S arrives second, yet still misunderstand why the time separation matters. Ask them to compare two hypothetical records with different intervals and to explain what would need to be known before estimating distance. Then give a trace with a clearly labelled data gap and see whether they mistakenly treat it as absence of shaking. Such exercises develop transferable reasoning and prevent diagrams from becoming picture-memory tests.
Students can practise by describing one seismic record in their strongest language and translating that description into a second language. The target should preserve observation, interpretation and uncertainty. Peer review can focus on whether a sentence accidentally turns signal amplitude into magnitude or changes an arrival into origin time. This approach connects science literacy to vocabulary, comprehension and technical writing without claiming that general language fluency alone is enough to interpret seismic data.
A compact expert-check workflow
Identify the record’s station, network, time standard, channel and plotted unit. Verify whether the trace is raw, filtered, normalised, clipped or truncated. Copy annotated phase picks exactly and separate them from unlabelled features. If an S–P interval is requested, compute it only from appropriate picks and label it as a time difference. Attribute event parameters to the monitoring report rather than deriving them from an image. Preserve uncertainty and preliminary status.
Finally review the translated text against the source for every time, unit, direction and measurement claim. Do not add a location, magnitude or damage conclusion that the supplied record does not justify. Ask a reviewer to reconstruct which waveform and event report the target refers to. If they cannot, restore the missing metadata or trim unsupported detail. A transparent, limited interpretation is a stronger educational product than a dramatic, confident misreading.
Twelve worked seismogram translation decisions
Worked example: two arrivals thirteen seconds apart
A hypothetical record identifies P at 10:00:24 and S at 10:00:37 on the same time standard. The S–P interval is thirteen seconds. A translated sentence should state exactly that, not that the earthquake occurred thirteen seconds earlier or thirteen kilometres away. Distance estimation requires an explicit travel-time model, and event origin time requires additional information. This tiny exercise demonstrates how one correct subtraction can be wrapped in an incorrect story if the variable being measured is not named. For multilingual readers, the words ‘delay’, ‘difference’, ‘arrival’ and ‘origin’ deserve separate glossary entries.
Worked example: a very tall trace from a close small event
A student compares two charts from different stations and says the taller one represents the greater earthquake magnitude. That inference ignores distance, gain, instrument characteristics and data processing. The safer translation is: ‘This displayed waveform has a larger plotted excursion than the other, but the charts are not directly comparable without scale and station context.’ If an official bulletin supplies magnitudes, quote those as separate event estimates. The lesson is not to distrust all amplitude measurements; it is to identify the chain that turns measurements into an event parameter.
Worked example: a helicorder row break
A public station display places one short time segment on each horizontal row. The trace approaches the right edge of a row, then resumes at the left edge of the next row. A translator mistakes the restart for a sudden seismic jump. A correct account explains that time continues onto the next displayed line, much like a line of text wraps on a page. The apparent discontinuity belongs to layout. This is a valuable reminder that graphics encode reading order in conventions that ordinary prose must make explicit when converted to another format.
Worked example: a tentative S pick
An analyst marks P with a solid symbol and S? with a question mark. The second annotation represents uncertainty, not a confirmed arrival. In the translation, ‘possible S-wave arrival’ preserves the source while ‘the S-wave started’ falsely removes doubt. If a computation uses the tentative pick, the result should be described as conditional on that selection. Scientific diagrams often carry their uncertainty in tiny marks, asterisks or footnotes. Language transfer fails when those marks disappear but the accompanying number survives as if nothing had changed.
Worked example: data gap rather than silence
A line goes flat for twenty seconds and resumes abruptly, with a small caption reading ‘telemetry missing’. The wrong explanation is ‘there was no ground movement for twenty seconds.’ The right explanation is that the recorder’s displayed data are missing for that interval. No physical conclusion about the ground can be drawn from those absent samples. When translating public data portals, preserving the difference between missing data and measured zero is particularly important. A blank or flat area can be an artefact of acquisition rather than a geophysical state.
Worked example: UTC date crossing
A waveform panel begins shortly before midnight UTC and continues into the next UTC date. A target translation gives both times but repeats the earlier date throughout, making the later arrival appear to precede the earlier one. A time-aware review catches this. State dates with times when the record crosses midnight, and indicate the time standard. If converting to local time, convert both dates consistently and label the conversion. Scientific chronology is part of the meaning, not an optional styling choice. Readers tracing event reports need the exact ordering.
Worked example: an unlabelled late wave train
A record shows several prominent oscillations after annotated P and S picks, but no additional phases are identified. The translator calls them ‘surface waves’ with absolute certainty. That may be plausible in some circumstances, yet the screenshot alone may not distinguish all phase contributions. Better: ‘A later wave train with larger excursions appears after the selected P and S arrivals; its components are not identified in the supplied figure.’ This sentence communicates the visual observation without fabricating a phase solution. The method generalises to any technical graph that invites over-interpretation.
Worked example: horizontal components differ
Two horizontal seismometer components show dissimilar amplitudes during the same time window. A translated narrative should not combine their largest values into one imaginary direction. Instead, name the channels and explain that recorded motion differs by component. If the station metadata shows orientations, they can be included. If not, retain the channel codes without guessing. This exercise shows the value of seemingly dry identifiers: they preserve which quantity was actually measured and protect later readers from false comparisons.
Worked example: magnitude and observed damage
A news graphic places an event magnitude beside an illustration of damaged buildings, while the seismogram itself only shows waves at one station. The translator must keep the source attributions distinct. The magnitude may be an official estimate; the illustration may be generic; the actual damage may require separate observation. A correct translation does not assert that the displayed waveform proves damage in a particular city. Readers deserve a clear distinction between measurement, modelled event properties and documented effects. This is both good science communication and responsible public information.
Worked example: the apparent first wiggle is noise
A faint oscillation appears before the analyst’s P-wave marker. A beginner shifts the pick left to the first non-flat pixel and calculates a longer S–P interval. However, background vibration or sensor noise can precede the selected seismic arrival. The correct translation preserves the chosen arrival annotation and, if discussing raw appearance, notes a lower-amplitude signal before it. Identifying an arrival is not the same as finding the earliest visible variation on the screen. This distinction helps students move from picture-reading to measurement reasoning.
Worked example: a clipped maximum
The top and bottom of a waveform flatten into straight sections while the source report flags clipping. The visible maximum is then a measurement limit, not necessarily the true ground-motion extreme. A translated phrase that says ‘maximum ground movement was exactly this value’ is too strong. Instead, explain that the recorded signal reaches the instrument or display limit and the original peak cannot be recovered from that trace alone. The missing amplitude information changes downstream calculations. Scientific translation must preserve the fact that a number can be bounded rather than fully measured.
Worked example: an outdated preliminary bulletin
A station chart circulated online with an early automatic event label. A later reviewed bulletin changes the estimated depth and magnitude. Translating the old screenshot without its issue time may imply the preliminary result is the final authoritative record. A careful caption states the data product’s date and preliminary status and, if comparing reports, distinguishes versions. Do not retroactively change the old document’s content under the guise of translation. Explain that event parameters can be updated when analysis incorporates additional observations. Provenance is part of accuracy.
A reader’s self-test
Can you distinguish a station arrival from an earthquake origin, a waveform amplitude from event magnitude, and an S–P time interval from a calculated source distance? Can you identify which channel, clock and unit a figure uses? Can you tell when a label represents an analyst’s interpretation rather than a visibly indisputable event? If you can answer those questions, you have learned the foundations for translating seismograms without inventing certainty.
Use an official educational record for practice and write two descriptions: a short one for a general reader and a longer one for a science student. Both should preserve the same times, phase names and limitations. Then compare the translation with the original. The goal is not to imitate the visual rhythm of a squiggly line but to explain what the measurement supports.
Continue the learning route
This guide owns the specific task of carrying seismogram evidence into reliable prose across languages. It complements the related translation guides on spectrograms, star charts and technical diagrams without repeating their central questions. For interpreting a wider range of language choices, follow eduKateSG’s Master Art of Translation. For vocabulary and the skill of making careful distinctions, explore the vocabulary learning routes.
For primary seismic context, consult a recognised monitoring authority such as the United States Geological Survey. Official waveform educational pages explain why arrivals, noise and station measurements must be interpreted carefully. Translators should use the strongest available source evidence, preserve uncertainties and attribute event conclusions to the organisation that actually made them.