Each guide begins with a short answer and follows one original record through definitions, calculations, evidence checks, changed contexts, misconceptions and bounded reporting.
The worked numbers are stipulated for learning. Authoritative sources define the operational concepts; the examples show how to keep their boundaries visible.
The worked records are original teaching examples. Each keeps the source state, transformation, output state and decision on separate lines so the reader can see exactly where interpretation begins.
A changed-context check alters one consequential condition while leaving the other inputs fixed. This makes transfer visible and prevents one numerical answer from becoming a rule outside its scope.
Keep a compact evidence receipt: object, method, units, reference condition, transformation, result and nearest rival explanation. A future reader should be able to reproduce the narrow claim.
The five reading routes move from definitions to mechanism, evidence, transfer and reporting. Readers may enter by task, but the examples remain connected rather than becoming detached tips.
The practical standard is an answer that can be checked. Preserve raw inputs, intermediate calculations, exclusions and versioned sources, then name one stronger claim the evidence cannot support.
Before choosing a formula, name the reader job in one sentence. A monitoring alert, research comparison, artistic rendering and teaching exercise may use the same observation differently.
Every central case includes a near-match with one familiar surface feature and a different mechanism underneath. A definition becomes useful when a learner can reject the tempting substitute.
The evidence route treats missing information honestly. An unknown method, interval, calibration or boundary stays blank until a source supplies it; an assumption may complete arithmetic while weakening the conclusion.
The transfer route changes scale, timing, composition or sampling without silently changing every other field. Predict the direction first, then calculate or inspect the result.
The reporting route keeps measurement and judgement separate. State what was observed, what rule produced the derived value, what uncertainty remains and which action follows only under declared conditions.
The final reader check is practical: the short answer states the distinction, the worked example can be reproduced, and the sources show where the example ends.
A useful misconception test constructs two cases with the same headline number and different underlying records. If their interpretations differ, the omitted condition belongs in the result.
Where a standard leaves behaviour to a competent analyst, observatory, laboratory or software workflow, the article says so directly. That boundary tells the reader which conclusion can travel.
The examples avoid hidden precision. Rounded display values remain linked to the unrounded calculation, and stipulated inputs are labelled as teaching data.
A complete explanation keeps three layers apart: the thing in the world, the method that turns it into a value, and the decision made from that value. Numerical agreement does not merge those layers.
For each central example, sketch the boundary before calculating. Mark what enters, what is transformed or excluded, what the instrument or algorithm can observe, and what must be inferred.
This specialist guide belongs to the Volcanology root. It also connects to The Gold Standard of Education | Learning That Transfers into Life and the How X Works hub. The worked cases are original teaching examples; their numbers are stipulated so that the reasoning can be checked.
eduKateSG · Volcanology
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Read the short answer first: earthquake magnitude estimates the size of a discrete source under a defined method; volcanic-tremor amplitude summarises a sustained signal at one station or across a network and depends on response, band, window, path and noise. Keep catalogue events and continuous metrics on separate timelines.
ROUTE 1 · CHAPTERS 1–4
Define the quantities
Name the quantities, reference conditions and reporting rules.
ROUTE 3 · CHAPTERS 9–12
Audit the evidence
Check instruments, algorithms, assumptions and rival explanations.
ROUTE 5 · CHAPTERS 17–20
Report and continue
Repair shortcuts, answer questions and follow verified routes.
Chapter contents
Define the quantities · Chapters 1–4
1. Name discrete earthquake magnitude and tremor amplitude
Work the mechanism · Chapters 5–8
5. Work the central mixed record
6. Keep logarithmic and linear summaries distinct
Audit the evidence · Chapters 9–12
10. Audit noise and non-volcanic sources
Transfer the reasoning · Chapters 13–16
13. Transfer to eruption monitoring
Report and continue · Chapters 17–20
18. Repair bigger amplitude means closer to eruption
CHAPTER 1 OF 20 · Define the quantities
1. Name discrete earthquake magnitude and tremor amplitude
Earthquake magnitude estimates the size of a discrete seismic source using a defined magnitude method. Volcanic tremor is a continuous or sustained seismic signal whose amplitude can be summarised at a station or network. A tremor-amplitude count is not automatically an earthquake magnitude.
Write the evidence in the order a reader can audit: the Volcanology quantity, its reference object, the observation or browser rule, the transformation, and the decision being made. Keeping those fields visible prevents a familiar label from hiding a changed basis.
A catalogue lists a magnitude 2.1 volcano-tectonic earthquake. The same hour has an RSAM mean of 380 instrument counts at station V01. Store them as different quantities.
First-principles test: ask what physical, observational or algorithmic operation produces each value in this chapter. Then ask whether the second value could change while the first stays fixed. If it can, the two labels are not substitutes. For Volcanology, this counterfactual is often clearer than a definition learned in isolation.
Keep the earthquake fixed and move the station farther away. RSAM amplitude can change while the event magnitude estimate is intended to represent the same source.
Evidence check: another reader should be able to reproduce the narrow result from the stored definitions, inputs and intermediate steps, then identify the nearest stronger claim that the evidence does not support.
Magnitude and amplitude methods depend on calibration, frequency band, network and source model.
CHAPTER 2 OF 20 · Define the quantities
2. Separate event boundaries from continuous windows
Magnitude calculation starts from an identified event with onset, phases and a source. Tremor metrics integrate or average signal over declared windows where individual events may be inseparable.
Trace the mechanism before interpreting the result. For Volcanology, mark which value belongs to the source, which belongs to the measurement or layout algorithm, and which is a reported summary. A calculation is useful only when those roles remain attached.
One ten-minute window contains continuous tremor and two small overlapping events. Record the window metric without inventing three magnitudes.
Practical transfer: build two records that share the headline number but differ in the condition discussed here. If the correct interpretation changes, the omitted condition is decision-relevant and belongs in the report. This test turns a vocabulary distinction into a reusable Volcanology checking habit.
Shorten the window to one minute and compare temporal detail.
Practical check: keep one counterexample beside the worked case. If the wording fails when that one condition changes, narrow the sentence until it describes only the evidence actually in hand.
Window summaries can hide bursts and gaps; retain waveforms and spectral evidence.
A seismometer converts ground motion through an instrument response. Raw counts depend on gain and response; corrected velocity, displacement or acceleration still depend on location, path and frequency content.
Use a compact decision table with columns for condition, input, operation, result and limit. This makes the comparison reproducible and exposes where a missing field would force an assumption instead of an observation.
Station V01 reports 380 counts and V02 120 for the same tremor. After response correction their physical amplitudes can be compared more meaningfully.
Misconception check: a plausible output does not prove the right reference, denominator, ancestor, spectrum or observation rule was used. Reconstruct one intermediate step and one changed-context prediction. If either cannot be stated, keep the result provisional rather than strengthening its wording.
Change only V01 gain in the teaching record. Raw counts change without a new volcanic source.
Transfer check: repeat the reasoning with one consequential condition changed while holding the rest fixed. State what changes, what stays comparable and why the original label alone was insufficient.
Clipping, telemetry gaps and noise can invalidate an amplitude summary.
A local, duration or moment magnitude uses particular waveform features, distance corrections and calibration. Magnitude is logarithmic and aims at source size, not the largest raw wiggle on one screen.
Preserve the raw inputs beside the derived result. If a later reader changes one condition, the original Volcanology reasoning should still be recoverable without reverse-engineering a rounded headline or an unlabeled screenshot.
A supplied local-magnitude calculation combines corrected amplitude and hypocentral distance to give ML 2.1.
Evidence design: retain both a positive case and a near-miss. The positive case shows when the rule applies; the near-miss changes one consequential condition and shows when the conclusion fails. Together they teach the boundary of the Volcanology mechanism better than another unlabelled example.
Keep source fixed and use another station; individual amplitudes differ while the network magnitude should remain compatible within uncertainty.
Audit check: retain the source version, units, settings, exclusions and rounding rule. A future correction should be able to alter one field without rebuilding the entire explanation from memory.
Different magnitude scales need not agree exactly and can saturate in different ranges.
The central hour contains one M2.1 earthquake, a second M1.4 event and sustained tremor whose RSAM rises from 120 to 380 counts at V01. The correct report keeps event magnitudes and windowed amplitude trend separate.
Ask what would have to stay fixed for the comparison to be fair. Record those controls explicitly, then name the first uncontrolled condition that could reverse the conclusion. This is the practical transfer step, not an optional footnote.
Build a timeline with catalogue rows and ten-minute RSAM rows rather than ranking 380 above 2.1.
Communication test: replace any sentence that says two things are “the same” or “different” with a sentence naming the operation, reference condition and supported consequence. The extra words are useful when they let a future reader repeat the decision without access to the original author.
Double station gain after minute thirty and show how an uncorrected RSAM jump appears without new source activity.
Decision check: end with an action or interpretation that follows from the stated conditions, followed by a boundary sentence explaining when a specialist rule, local procedure or additional measurement is needed.
The numbers are invented and do not describe a real volcano or forecast.
CHAPTER 6 OF 20 · Work the mechanism
6. Keep logarithmic and linear summaries distinct
A one-unit magnitude increase represents a multiplicative change under the chosen scale. RSAM may be a mean absolute amplitude in counts or corrected units over time. Their axes and transformations are unrelated.
Write the evidence in the order a reader can audit: the Volcanology quantity, its reference object, the observation or browser rule, the transformation, and the decision being made. Keeping those fields visible prevents a familiar label from hiding a changed basis.
Compare M1.4 and M2.1 only within the same magnitude convention; compare 120 and 380 only within a stable RSAM chain.
First-principles test: ask what physical, observational or algorithmic operation produces each value in this chapter. Then ask whether the second value could change while the first stays fixed. If it can, the two labels are not substitutes. For Volcanology, this counterfactual is often clearer than a definition learned in isolation.
Take a logarithm of RSAM for plotting and explain why that still does not create earthquake magnitude.
Evidence check: another reader should be able to reproduce the narrow result from the stored definitions, inputs and intermediate steps, then identify the nearest stronger claim that the evidence does not support.
Plotting choices do not change the physical definition.
Network upgrades, sensor types and digitiser gain can create steps in amplitude time series. Corrected long-term comparison needs response metadata and overlap checks.
Trace the mechanism before interpreting the result. For Volcanology, mark which value belongs to the source, which belongs to the measurement or layout algorithm, and which is a reported summary. A calculation is useful only when those roles remain attached.
Replace V01 with a broadband sensor during the central record and mark the discontinuity.
Practical transfer: build two records that share the headline number but differ in the condition discussed here. If the correct interpretation changes, the omitted condition is decision-relevant and belongs in the report. This test turns a vocabulary distinction into a reusable Volcanology checking habit.
Run old and new sensors side by side for one week.
Practical check: keep one counterexample beside the worked case. If the wording fails when that one condition changes, narrow the sentence until it describes only the evidence actually in hand.
Response removal can amplify noise outside the reliable passband.
Amplitude decays and changes spectrum with source-station distance, geology and topography. A station near a vent may show larger tremor than a farther station even when source strength is unchanged.
Use a compact decision table with columns for condition, input, operation, result and limit. This makes the comparison reproducible and exposes where a missing field would force an assumption instead of an observation.
V01 is 3 km from the source region and V02 is 12 km; their raw RSAM values differ.
Misconception check: a plausible output does not prove the right reference, denominator, ancestor, spectrum or observation rule was used. Reconstruct one intermediate step and one changed-context prediction. If either cannot be stated, keep the result provisional rather than strengthening its wording.
Use amplitude ratios from several stations to constrain a source location under a declared model.
Transfer check: repeat the reasoning with one consequential condition changed while holding the rest fixed. State what changes, what stays comparable and why the original label alone was insufficient.
Changing attenuation and scattering can break a simple distance rule.
Volcanic tremor, cultural noise, wind and regional earthquakes occupy overlapping but different spectral regions. RSAM and SSAM filters determine which energy contributes to the summary.
Preserve the raw inputs beside the derived result. If a later reader changes one condition, the original Volcanology reasoning should still be recoverable without reverse-engineering a rounded headline or an unlabeled screenshot.
Compute a broad-band RSAM and three spectral bands for the same hour. A low-frequency rise appears in only one band.
Evidence design: retain both a positive case and a near-miss. The positive case shows when the rule applies; the near-miss changes one consequential condition and shows when the conclusion fails. Together they teach the boundary of the Volcanology mechanism better than another unlabelled example.
Shift the filter cutoff and inspect whether the trend survives.
Audit check: retain the source version, units, settings, exclusions and rounding rule. A future correction should be able to alter one field without rebuilding the entire explanation from memory.
Band energy alone does not uniquely identify magma or gas movement.
Wind, rivers, vehicles, ocean noise, quarry blasts and distant earthquakes can raise seismic amplitude. Network coherence, timing, spectra and other monitoring data help separate them.
Ask what would have to stay fixed for the comparison to be fair. Record those controls explicitly, then name the first uncontrolled condition that could reverse the conclusion. This is the practical transfer step, not an optional footnote.
A storm raises amplitude at one exposed station but not the sheltered network.
Communication test: replace any sentence that says two things are “the same” or “different” with a sentence naming the operation, reference condition and supported consequence. The extra words are useful when they let a future reader repeat the decision without access to the original author.
Compare the same weather interval across stations before labelling tremor.
Decision check: end with an action or interpretation that follows from the stated conditions, followed by a boundary sentence explaining when a specialist rule, local procedure or additional measurement is needed.
Some regional signals can appear coherent, so expert review remains necessary.
Strong signals can exceed the recorder range and flatten waveforms. A clipped RSAM may understate change or become incomparable with unclipped periods.
Write the evidence in the order a reader can audit: the Volcanology quantity, its reference object, the observation or browser rule, the transformation, and the decision being made. Keeping those fields visible prevents a familiar label from hiding a changed basis.
The central 380-count window contains flat-topped samples. Flag it rather than treating 380 as an exact maximum.
First-principles test: ask what physical, observational or algorithmic operation produces each value in this chapter. Then ask whether the second value could change while the first stays fixed. If it can, the two labels are not substitutes. For Volcanology, this counterfactual is often clearer than a definition learned in isolation.
Lower gain on a parallel channel and test whether the signal is recovered.
Evidence check: another reader should be able to reproduce the narrow result from the stored definitions, inputs and intermediate steps, then identify the nearest stronger claim that the evidence does not support.
Clipping repair may be impossible without an unsaturated channel.
Small discrete earthquakes may be missed when tremor or noise is high. A falling event count during rising tremor does not prove earthquakes stopped.
Trace the mechanism before interpreting the result. For Volcanology, mark which value belongs to the source, which belongs to the measurement or layout algorithm, and which is a reported summary. A calculation is useful only when those roles remain attached.
During the 380-count interval, the detection threshold rises from M0.5 to M1.2 in the teaching record.
Practical transfer: build two records that share the headline number but differ in the condition discussed here. If the correct interpretation changes, the omitted condition is decision-relevant and belongs in the report. This test turns a vocabulary distinction into a reusable Volcanology checking habit.
Compare counts above a common completeness threshold.
Practical check: keep one counterexample beside the worked case. If the wording fails when that one condition changes, narrow the sentence until it describes only the evidence actually in hand.
Completeness estimates are uncertain and time-dependent.
Observatories combine seismic event types, tremor, deformation, gas, thermal and visual evidence. Rising amplitude is one line of evidence, not a deterministic eruption alarm.
Use a compact decision table with columns for condition, input, operation, result and limit. This makes the comparison reproducible and exposes where a missing field would force an assumption instead of an observation.
Pair the RSAM rise with unchanged deformation and gas in one scenario, then with coordinated changes in another.
Misconception check: a plausible output does not prove the right reference, denominator, ancestor, spectrum or observation rule was used. Reconstruct one intermediate step and one changed-context prediction. If either cannot be stated, keep the result provisional rather than strengthening its wording.
Keep RSAM identical while altering the other evidence.
Transfer check: repeat the reasoning with one consequential condition changed while holding the rest fixed. State what changes, what stays comparable and why the original label alone was insufficient.
Only the responsible observatory issues current alerts and interpretations.
Long-duration tremor may be located using relative amplitudes across stations when phase picks are unavailable. The method needs attenuation assumptions and calibrated station responses.
Preserve the raw inputs beside the derived result. If a later reader changes one condition, the original Volcanology reasoning should still be recoverable without reverse-engineering a rounded headline or an unlabeled screenshot.
Use three teaching stations with amplitude decay to estimate an approximate source zone.
Evidence design: retain both a positive case and a near-miss. The positive case shows when the rule applies; the near-miss changes one consequential condition and shows when the conclusion fails. Together they teach the boundary of the Volcanology mechanism better than another unlabelled example.
Move one station in the model and recompute.
Audit check: retain the source version, units, settings, exclusions and rounding rule. A future correction should be able to alter one field without rebuilding the entire explanation from memory.
Amplitude-based locations can be biased by site effects and changing source spectra.
A swarm rate counts discrete events above a stated threshold, while tremor amplitude summarises sustained signal. Both can rise together or move independently.
Ask what would have to stay fixed for the comparison to be fair. Record those controls explicitly, then name the first uncontrolled condition that could reverse the conclusion. This is the practical transfer step, not an optional footnote.
Plot hourly event rate beside RSAM and identify intervals of agreement and divergence.
Communication test: replace any sentence that says two things are “the same” or “different” with a sentence naming the operation, reference condition and supported consequence. The extra words are useful when they let a future reader repeat the decision without access to the original author.
Raise the catalogue threshold and observe event rate fall without changing RSAM.
Decision check: end with an action or interpretation that follows from the stated conditions, followed by a boundary sentence explaining when a specialist rule, local procedure or additional measurement is needed.
Correlation does not identify a common source mechanism.
CHAPTER 16 OF 20 · Transfer the reasoning
16. Transfer across stations and volcanoes
Raw amplitude scales are rarely portable across instruments, distances and volcanoes. Normalisation and local baselines can support trend comparison, but they do not produce a universal eruption intensity scale.
Write the evidence in the order a reader can audit: the Volcanology quantity, its reference object, the observation or browser rule, the transformation, and the decision being made. Keeping those fields visible prevents a familiar label from hiding a changed basis.
Station A baseline is 20 counts and Station B 200; each triples during unrest. Compare relative change with caution.
First-principles test: ask what physical, observational or algorithmic operation produces each value in this chapter. Then ask whether the second value could change while the first stays fixed. If it can, the two labels are not substitutes. For Volcanology, this counterfactual is often clearer than a definition learned in isolation.
Swap instruments between sites and rebuild baselines.
Evidence check: another reader should be able to reproduce the narrow result from the stored definitions, inputs and intermediate steps, then identify the nearest stronger claim that the evidence does not support.
Geology and noise make even normalized changes context-specific.
Calling an RSAM peak “tremor magnitude 380” borrows a source-size word for an instrument-window statistic. Report the amplitude metric, units, station and window instead.
Trace the mechanism before interpreting the result. For Volcanology, mark which value belongs to the source, which belongs to the measurement or layout algorithm, and which is a reported summary. A calculation is useful only when those roles remain attached.
Rewrite the central label as “V01 ten-minute mean absolute amplitude: 380 counts, broad band, response unchanged.”
Practical transfer: build two records that share the headline number but differ in the condition discussed here. If the correct interpretation changes, the omitted condition is decision-relevant and belongs in the report. This test turns a vocabulary distinction into a reusable Volcanology checking habit.
Convert counts to corrected velocity and keep the result a station amplitude.
Practical check: keep one counterexample beside the worked case. If the wording fails when that one condition changes, narrow the sentence until it describes only the evidence actually in hand.
Some research defines specialised tremor magnitudes; use only the published method and calibration.
CHAPTER 18 OF 20 · Report and continue
18. Repair bigger amplitude means closer to eruption
Amplitude can rise because of source strength, source location, path, instrument, noise or overlapping events. Forecast meaning comes from a validated pattern and multiple lines of evidence.
Use a compact decision table with columns for condition, input, operation, result and limit. This makes the comparison reproducible and exposes where a missing field would force an assumption instead of an observation.
A passing regional earthquake produces the largest amplitude of the day without volcanic change.
Misconception check: a plausible output does not prove the right reference, denominator, ancestor, spectrum or observation rule was used. Reconstruct one intermediate step and one changed-context prediction. If either cannot be stated, keep the result provisional rather than strengthening its wording.
Remove the regional interval and reassess the volcanic trend.
Transfer check: repeat the reasoning with one consequential condition changed while holding the rest fixed. State what changes, what stays comparable and why the original label alone was insufficient.
Past patterns may not repeat across eruptions or volcanoes.
Store station, coordinates, sensor and digitiser response, gain, sampling, band, correction, window, statistic, clipping, gaps, noise flags, event catalogue, magnitude method, locations, completeness and other monitoring evidence.
Preserve the raw inputs beside the derived result. If a later reader changes one condition, the original Volcanology reasoning should still be recoverable without reverse-engineering a rounded headline or an unlabeled screenshot.
Package the central two-event plus tremor hour so another analyst can recreate the separate graphs.
Evidence design: retain both a positive case and a near-miss. The positive case shows when the rule applies; the near-miss changes one consequential condition and shows when the conclusion fails. Together they teach the boundary of the Volcanology mechanism better than another unlabelled example.
Delete the gain-change log and ask which amplitude trend becomes unreliable.
Audit check: retain the source version, units, settings, exclusions and rounding rule. A future correction should be able to alter one field without rebuilding the entire explanation from memory.
A screenshot of a seismogram cannot reproduce the processing chain.
A defensible report names discrete event magnitudes separately from station or network tremor amplitude, states all units and windows, and avoids predicting eruption from either alone.
Ask what would have to stay fixed for the comparison to be fair. Record those controls explicitly, then name the first uncontrolled condition that could reverse the conclusion. This is the practical transfer step, not an optional footnote.
Write: “Two catalogue events were M2.1 and M1.4; V01 RSAM rose from 120 to 380 counts in ten-minute windows. The quantities describe different seismic summaries.”
Communication test: replace any sentence that says two things are “the same” or “different” with a sentence naming the operation, reference condition and supported consequence. The extra words are useful when they let a future reader repeat the decision without access to the original author.
Change the station response and identify which amplitude series must be recalculated.
Decision check: end with an action or interpretation that follows from the stated conditions, followed by a boundary sentence explaining when a specialist rule, local procedure or additional measurement is needed.
Public hazard decisions require the current volcano-observatory assessment.
Continue through the verified reading route
Event rates and magnitude thresholds
Event rates and magnitude thresholds. Use this for catalogue counts, completeness and common-threshold comparisons.
Source depth and volume change
Source depth and volume change. Use this when one deformation amplitude is treated as a unique source.
Gas concentration and emission rate
Gas concentration and emission rate. Use this for local concentration versus integrated source flux.
Column height and downwind plume position
Column height and downwind plume position. Use this when vertical source behaviour and transported cloud location are merged.
Frequently asked questions
Can an RSAM value be called a tremor magnitude?
Only if a specific published and calibrated tremor-magnitude method is used. Ordinary RSAM is a station or network amplitude statistic.
Why can the same tremor have different station amplitudes?
Instrument response, distance, path, site effects, frequency band and noise differ among stations.
Does rising tremor amplitude predict an eruption?
It is one monitoring signal. Observatories interpret it with event type, deformation, gas, thermal, visual and historical evidence.
Authoritative sources and further reading
USGS: Monitoring volcano seismicity. The official overview distinguishes volcano-tectonic earthquakes, long-period events and continuous tremor.
USGS: Real-time seismic amplitude measurement. The original RSAM research describes continuous average absolute amplitude monitoring and its instrument limitations.
USGS: Earthquake magnitude measurement. The official explanation separates station ground motion, earthquake magnitude and location-dependent intensity.
USGS SIR 2024-5062B: Volcano seismic techniques. The current technical report covers discrete earthquakes, tremor, networks, processing and monitoring instrumentation.
Return to the Volcanology subject guide, The Gold Standard of Education, or the How X Works hub.