Refining origins¶
The REFINE panel holds the tools that work on origins. They are grouped on four tabs: Relocate, DD, Swarm and QC. The QC tab is described in Quality control.
Most tools work on the active origin, the origin selected in the origin table, or on all selected origins. The buttons show what a click will do, for example “Smart-locate 12” with twelve origins selected or “Smart-locate all (340)” with none.
Relocate tab¶
Relocation¶
Control |
Description |
|---|---|
Interface |
Locator, for example LOCSAT. Azimuth locates from back-azimuths only. Single DD relocates by double difference against the reference catalogue of the DD tab. |
Profile |
Locator profile: the velocity model or travel-time set. |
Fix depth [km] |
Keep the depth fixed at the given value. |
Ignore initial location |
Do not use the current location as the starting point. |
MC draws, min set |
Monte Carlo rescue used by Smart-locate: number of random pick subsets and the smallest subset size. |
Fast smart-locate |
Accept the first converged solution instead of climbing the whole recovery ladder. |
Consider virtual picks |
Add the source picks of virtual picks as arrivals with weight 0. |
Relocate relocates the active origin and shows the result as a candidate in the diagnostic plots. Press Accept origin to keep it: it replaces the origin and is marked as updated. With two or more origins selected, each is relocated and accepted directly.
Smart-locate associates, relocates and rescues an origin automatically, following the analyst’s decision rules. With one origin the result is a candidate to review; with several, each successful result is accepted. See Analyst rules and Smart-locate.
Reset replaces the active origin with its first stored solution and undoes all later relocations.
Association¶
Control |
Description |
|---|---|
Associate |
Add unassociated picks to the selected origins when their travel-time residual is within Assoc. tol. |
Deassociate |
Remove arrivals whose residual is larger than Assoc. tol. |
New from sel. |
Create a new candidate origin from the picks box-selected on the Travel-time plot, for example when a second event appears there. The current origin is not changed. |
Drop dup. sta. |
Remove the picks of every station that has two or more picks of the same phase in the origin. The next association brings back the one that fits. |
Assoc. tol [s] |
Largest travel-time residual for association. |
TTT, TTT model |
Travel-time interface and model for predicted times, residuals and plots. |
Max distance [km] |
Do not associate picks from stations farther away. 0 = no limit. |
Picks can also be associated by hand: box-select blue (unassociated) picks on the Travel-time, Distance or Azimuth plot of the active origin.
Merging¶
Merge origins combines origins that describe the same event. Two origins are merged when
their hypocentres are closer than Merge dist [km] (3D distance) and their origin times differ by less than Merge time [s], or
they share at least Min shared picks picks, wherever they are located. Two arrivals count as the same pick when they are on the same station and phase and their times agree within Pick match [s].
The origin that is kept is chosen by the ranking under Preferred origin when
merging. The criteria are compared from top to bottom, and a tie falls
through to the next. Numeric criteria prefer higher or lower values;
Author and Method prefer a named author or method. The ranking is saved in
the profile as preferRules.
DD tab: double-difference relocation¶
The DD tab relocates origins with the double-difference method [12], against a fixed reference catalogue or relative to one another.
Load a reference catalogue with Load XML…: a SeisComP EventParameters XML file with origins and their picks.
Choose Single DD as the locator interface on the Relocate tab to relocate single origins against the reference, or select several origins and press Multi-event DD relocate (selected) to relocate them relative to one another. New origins are added; the originals are kept.
Parameter |
Description |
|---|---|
Neighbours |
Nearest neighbours paired with each event. |
Max pair [km] |
Only pair events within this 3D distance. |
Iterations |
Gauss–Newton iterations. |
Damping |
Levenberg damping. Higher values keep events closer to their start, which anchors the absolute position. |
Min depth [km] |
Soft floor that keeps events below this depth instead of pinning them at 0. Useful for nucleations that start at the surface. |
Max step [km] |
Limit on how far an event may move per iteration. 0 = no limit. |
Max resid [s] |
Differential times with a larger residual are rejected. Also the scale of the DD qual metric. |
Weight by distance |
Down-weight distant event pairs. |
Fix depth |
Keep the depths fixed. |
Auto derives the data-driven parameters, such as Max pair, from the selected origins.
The origin table shows the result as DD ties (number of accepted differential times), DD res (their residual) and DD qual (0 = good, 1 = bad).
Swarm tab: recovering further events¶
During swarms and aftershock sequences many events are recorded by only a few stations and are missed by nucleation. The Swarm tab finds them by comparing unused picks with the arrival patterns of well-located events. The recovered events are added as preliminary origins; locate them afterwards with Smart-locate all.
Template match¶
With one origin selected, it is used as a template to find repeats of that event. With none or several selected, the origins are clustered (within Spatial radius), and per cluster the relative arrival-time pattern of the best-recorded origin is matched against the unused picks.
Swarm consensus¶
Learns the median relative arrival-time pattern of each origin cluster and searches the unused picks for the same pattern.
Parameter |
Description |
|---|---|
Spatial radius [km] |
How close two epicentres must be to belong to the same swarm. Depth and time are ignored. |
Min. core events |
Minimum number of well-located events a cluster needs to serve as a reference. |
Min. matching phases |
Minimum matched information for a candidate: each matched P or S counts 1; an array pick adds 1 for back-azimuth and 1 for slowness. |
Time tolerance [s] |
Largest origin-time residual for a pick to support a candidate. |
Iterate until stable |
After accepting and relocating new events, update the swarm model and repeat until nothing new is found. |
Match Slow/Baz¶
For array picks with back-azimuth and slowness. A source that is active repeatedly, such as a quarry, produces the same slowness vector at an array every time. Match Slow/Baz uses the selected origin as a template and gives its location to every pick whose array measured the same slowness vector within the tolerance. Only selected picks are tested, or all picks if none are selected.
Known sources can be kept in a CSV source catalogue
(source_id, lat, lon, depth, net, sta, backazimuth, slowness):
Save Source appends the selected origin to the catalogue, one row per array signature.
Load catalog… loads a catalogue. Its path is saved in the profile (
bearingCatalog), so each profile can have its own list of known sources.With Consider reference catalog, candidates are also matched against every source in the catalogue.
Fingerprint match¶
Recovers weak origins, recorded by only a few stations, by matching their relative arrival times against trusted anchor origins recorded by many stations.
Parameter |
Description |
|---|---|
Anchor min. stations |
Origins with at least this many stations are anchors. |
Target max. stations |
Origins with at most this many stations are targets. |
Min. shared stations |
Stations a target must share with an anchor. Two gives the highest recall; three is safer. |
Time tolerance [s] |
Matching tolerance per station. |
Agree fraction |
Fraction of shared stations whose timing must agree. |
Accept max. spread [km] |
Reject the result when the matched anchors are farther apart. |
Inherit anchor depth |
Use the median depth of the matched anchors. |
Origin table actions¶
The context menu of the origin table offers:
Copy and Save as CSV… of the selected rows,
Delete origin(s),
Review in scolv: send the origin and its picks to scolv for review. Requires a messaging connection.
Shift+double-click stars or unstars an origin. Stars mark origins for later review, for example by the QC rules.