Glossary

This glossary defines key seismological and technical terms used throughout the Earthquake Catalogue Platform documentation.

Seismological Terms

aftershock: An earthquake that follows a larger earthquake (the mainshock) in the same geographic area. Aftershocks typically decrease in frequency and magnitude over time following the Omori-Utsu law.
arrival time: The time at which a seismic wave is recorded at a seismic station. P-wave arrivals are typically used for initial event detection.
azimuthal gap: The largest angle (in degrees) between adjacent seismic stations as viewed from the earthquake epicenter. Smaller gaps (< 180°) indicate better station coverage and more reliable locations. Gaps > 240° often result in poorly constrained locations.
b-value: The slope of the frequency-magnitude distribution (Gutenberg-Richter relation). Typically around 1.0 for tectonic earthquakes. Higher b-values indicate a greater proportion of small earthquakes relative to large ones.
body wave magnitude (mb): A magnitude scale based on the amplitude of P-waves, typically used for teleseismic events (distance > 20°).
completeness magnitude (Mc): The minimum magnitude above which all earthquakes in a region are reliably detected and recorded. Events below Mc may be missing from the catalogue. Essential for statistical analyses like b-value calculation.
depth: The vertical distance from the Earth’s surface to the earthquake hypocenter, measured in kilometers. Shallow events (< 70 km), intermediate (70-300 km), and deep (> 300 km) earthquakes have different characteristics.
epicenter: The point on the Earth’s surface directly above the earthquake hypocenter. Specified by latitude and longitude coordinates.
evaluation mode: Indicates whether an earthquake solution is automatic (computed by software) or manual (reviewed by a seismologist). Manual solutions are typically more reliable.
evaluation status: The review status of an earthquake solution: preliminary, confirmed, reviewed, or final. Final solutions represent the most thoroughly reviewed data.
event type: Classification of a seismic event, such as earthquake, explosion, quarry blast, volcanic, induced, or not existing.
focal mechanism: A mathematical description of the fault orientation and slip direction for an earthquake, commonly visualized as a “beach ball” diagram showing compressional and dilatational first motions.
foreshock: An earthquake that precedes a larger earthquake (the mainshock) in the same area. Foreshocks cannot be identified until after the mainshock occurs.
Gutenberg-Richter relation: An empirical relationship describing the frequency-magnitude distribution of earthquakes: log₁₀(N) = a - bM, where N is the number of events with magnitude ≥ M, and a and b are constants.
hypocenter: The three-dimensional location of earthquake rupture initiation, specified by latitude, longitude, and depth. Also called the focus.
intensity: A measure of earthquake shaking at a specific location based on observed effects and damage. Measured on scales like Modified Mercalli Intensity (MMI).
local magnitude (ML): The original magnitude scale developed by Charles Richter for Southern California, based on the maximum amplitude recorded on a Wood-Anderson seismograph.
magnitude: A quantitative measure of earthquake size, typically based on recorded ground motion amplitude. Various magnitude scales exist (ML, Mw, mb, Ms).
magnitude type: The specific magnitude scale used for measurement, such as ML (local), Mw (moment), mb (body wave), or Ms (surface wave).
mainshock: The largest earthquake in a sequence of events occurring in a specific area and time window.
moment magnitude (Mw): A magnitude scale based on seismic moment, which is proportional to fault area × average slip × rock rigidity. Preferred for large earthquakes as it does not saturate at high magnitudes.
origin time: The time at which earthquake rupture initiated at the hypocenter.
P-wave: Primary (or compressional) wave - the fastest type of seismic body wave. P-waves travel through both solid and liquid media and arrive first at seismic stations.
phase: A distinct seismic wave arrival at a station, such as P, S, or surface waves. Multiple phases from multiple stations constrain earthquake locations.
pick: The identified arrival time of a seismic phase at a station, either automatically detected or manually identified by an analyst.
quality score: A numerical assessment (0-100) of earthquake location and magnitude reliability based on factors like station coverage, uncertainties, and solution parameters.
residual: The difference between observed and predicted arrival times. Small residuals indicate a good velocity model and accurate location.
RMS residual: Root Mean Square of travel time residuals. A measure of overall fit quality for an earthquake location. Lower values indicate better solutions.
S-wave: Secondary (or shear) wave - slower than P-waves and cannot travel through liquids. S-wave arrivals help constrain earthquake depth.
seismic moment: A physical measure of earthquake size defined as M₀ = μ × A × D, where μ is rock rigidity, A is fault area, and D is average slip. Related to moment magnitude by Mw = (log₁₀(M₀) - 9.1) / 1.5.
station coverage: The spatial distribution and density of seismic stations around an earthquake. Good coverage (many well-distributed stations) improves location accuracy.
surface wave magnitude (Ms): A magnitude scale based on the amplitude of surface waves, typically used for shallow teleseismic events.
swarm: A sequence of many earthquakes occurring in a limited area and time without a clearly dominant mainshock.
uncertainty ellipse: An ellipse (or ellipsoid in 3D) representing the statistical uncertainty in earthquake location, typically at a specified confidence level (e.g., 95%).
used phase count: The number of seismic phase arrivals used in determining an earthquake location. More phases generally result in more accurate and better-constrained locations.
used station count: The number of seismic stations whose data contributed to the earthquake location solution. More stations typically improve location accuracy.

Technical Terms

API: Application Programming Interface. A set of protocols and tools for building software applications. The platform provides a REST API for programmatic access.
catalogue: A collection of earthquake events stored with shared metadata and consistent schema. Catalogues can be uploaded, imported from external sources, merged, and exported.
CSV: Comma-Separated Values. A plain text format for tabular data where values are separated by commas (or other delimiters).
FDSN: International Federation of Digital Seismograph Networks. An organization that develops standards for seismic data exchange, including web services for event data.
GeoJSON: A format for encoding geographic data structures using JSON. Events are represented as Point features with properties.
GeoNet: New Zealand’s official geological hazard monitoring system, operated by GNS Science. Provides real-time earthquake data via FDSN web services.
JSON: JavaScript Object Notation. A lightweight data interchange format that is easy for humans to read and write and for machines to parse and generate.
merge: The process of combining multiple earthquake catalogues into a single catalogue, with automated duplicate detection and conflict resolution.
MongoDB: A document-oriented NoSQL database used by the platform to store earthquake events and catalogues.
Next.js: A React-based web framework used for the platform’s frontend and API routes.
QuakeML: An XML-based standard developed by the seismological community for exchanging earthquake event data. The platform supports QuakeML 1.2 BED (Basic Event Description) format.
REST: Representational State Transfer. An architectural style for web APIs using HTTP methods (GET, POST, PUT, DELETE) to perform operations on resources.
RTD: Read the Docs. A documentation hosting platform that automatically builds and publishes Sphinx documentation from version control repositories.
schema: The structure and organization of data, defining what fields are present, their types, and validation rules.
Sphinx: A documentation generator that converts reStructuredText files into various output formats including HTML, PDF, and ePub.
UUID: Universally Unique Identifier. A 128-bit identifier used to uniquely identify catalogues and events in the database.
validation: The process of checking data against defined rules and constraints to ensure quality and consistency before storage.

Quality Grades

A+ grade: Excellent quality (95-100 score). Publication-quality data with comprehensive metadata, small uncertainties, and excellent station coverage.
A grade: Excellent quality (90-94 score). High-quality, reliable data suitable for most research applications.
B grade: Good quality (80-89 score). Suitable for general analysis with minor limitations in some parameters.
C grade: Fair quality (70-79 score). Acceptable for preliminary analysis but may have significant uncertainties or missing metadata.
D grade: Poor quality (60-69 score). Use with caution; significant data quality issues may affect analysis results.
F grade: Failing quality (< 60 score). Insufficient quality for reliable analysis; data should be reviewed and improved before use.