Tectonic Motions in California Inferred from Very Long Baseline Interferometry Observations

Vocabulary flashcards summarizing essential terms and concepts related to Very Long Baseline Interferometry (VLBI) and its application to tectonic studies.

Very Long Baseline Interferometry (VLBI)

A microwave-based space-geodetic technique that determines the difference in arrival times of radio signals at multiple telescopes to derive precise positions and Earth orientation.

Microwave-based space geodetic technique

A measurement method that uses microwave radio waves to study Earth’s geometry and motion from space; VLBI is an example.

Extragalactic radio source

A distant celestial object (e.g., quasar) outside the Milky Way that emits strong radio waves used as reference points in VLBI.

Quasar

An extremely bright, distant active galactic nucleus commonly used as a stable radio source for VLBI observations.

Baseline (in VLBI)

The distance between two radio telescopes, often thousands of kilometers long, calculated from measured time delays.

Time delay

The difference in arrival times of a radio signal at two separate telescopes; key observable used to compute baselines in VLBI.

Cross-correlation

The signal-processing step that compares recorded waveforms from different telescopes to detect time delays in VLBI.

Atomic clock

An ultra-stable timing device (e.g., hydrogen maser) that records exact signal arrival times at each VLBI station.

Hydrogen maser

A highly stable type of atomic clock essential for precise timing in VLBI observations.

International Terrestrial Reference Frame (ITRF)

A global coordinate system whose orientation and scale are refined using VLBI measurements of Earth’s rotation and station positions.

Long-term stability (VLBI advantage)

The ability of VLBI to maintain millimeter-level precision for years to decades, ideal for tracking slow tectonic motions.

Extremely high precision (VLBI advantage)

VLBI can detect baseline changes of just a few millimeters over thousands of kilometers.

Sparse global network (VLBI limitation)

Relatively few VLBI stations worldwide, leading to limited spatial coverage compared with denser networks like GPS.

Limited temporal resolution (VLBI limitation)

Observations are scheduled infrequently, often weeks apart, making it difficult to capture rapid events such as immediate post-earthquake deformation.

Tectonic motion measurement with VLBI

Using long-term, high-precision baseline changes between stations to quantify plate movements and deformation.