SCDetect - Computationally efficient earthquake detection

Content

• About
• Overview
• Getting started
  • General
  • Template configuration
  • Inventory metadata, event metadata and configuration
  • Waveform data and RecordStream configuration
• Installation
• Tests
• Issues
• Contributions
• License

About

scdetect is a SeisComP extension module that implements both real-time and classical offline earthquake detection based on waveform cross-correlation, also called matched filtering or template matching.

The module allows both single-stream and multi-stream earthquake detection.

In case the detection parameters exceed the configured thresholds, scdetect declares a new origin.

Overview

Above, the modular organization of SeisComP with messaging system (mediator), RecordStream interface (waveform server) and database including scdetect's role in the SeisComP overall architecture. In SeisComP language scdetect is a representative for a trunk module.

From an architectural point of view scdetect is positioned somewhere between scautopick and scautoloc. That is, scdetect fetches waveform data by means of the RecordStream interface, but it also uses data products for template generation.

For further information with regards to the SeisComP architecture please refer to the SeisComP documentation.

Getting started

General

As scdetect is a standard SeisComP extension module a list of available commandline options can be obtained with

$ scdetect -h

For a general more in-depth introduction on how to use SeisComP modules including their particular configuration, please refer to the SeisComP documentation.

The subsequent sections are intented to provide an introduction on how to use and configure scdetect. This includes:

1. How to configure templates
2. How to access metadata and configuration from the database or from plain files
3. How waveform data is accessed including both template waveform data caching and template waveform data preparation

Template configuration

In order to run scdetect a template configuration must be provided. That is, either by means of the templatesJSON configuration option in one of scdetect's module configuration files or by means of using scdetect's --templates-json path/to/templates.json CLI flag.

The template configuration itself is a JSON configuration file and contains an array of detector configuration JSON objects (each detector refers to a template event identified by its "originId"). An exemplary multi-stream detector configuration (for the streams CH.GRIMS..HHZ and CH.HASLI..HHZ) may look like:

    {
        "detectorId": "detector-01",
        "createArrivals": true,
        "createTemplateArrivals": true,
        "gapInterpolation": true,
        "gapThreshold": 0.1,
        "gapTolerance": 1.5,
        "triggerDuration": -1,
        "triggerOnThreshold": 0.98,
        "triggerOffThreshold": 0,
        "originId": "smi:ch.ethz.sed/sc3a/origin/NLL.20201026144442.91156.194937",
        "filter": "",
        "templateFilter": "",
        "streams": [
              {
                  "templateId": "template-01",
                  "initTime": 10,
                  "templateWaveformStart": -2,
                  "templateWaveformEnd": 2,
                  "waveformId": "CH.GRIMS..HHZ",
                  "templateWaveformId": "CH.GRIMS..HHZ",
                  "templatePhase": "Pg"
              },
              {
                  "templateId": "template-02",
                  "initTime": 10,
                  "templateWaveformStart": -3,
                  "templateWaveformEnd": 1,
                  "waveformId": "CH.HASLI..HHZ",
                  "templateWaveformId": "CH.HASLI..HHZ",
                  "templatePhase": "Pg"
              }
        ]
    }

That is, a detector configuration defines besides the detector specific configuration parameters a list of stream configurations and optionally some stream configuration defaults.

NOTE: scdetect is operating strictly stream based. For this reason station bindings are not supported (in contrast to other SeisComP modules such as e.g. scautopick, etc.)

Note that if a configuration parameter is not explicitly defined a module specific global default is used instead. Global defaults may be configured following SeisComP's standard module configuration approach. That is, by means of either global or module specific configuration files (global.cfg, scdetect.cfg located at corresponding configuration directory paths).

In order to validate the template configuration, with templates.schema.json a rudimentary JSON schema is provided.

Detector configuration parameters

A detector configuration allows to set the following detector specific configuration parameters:

General:

• "detectorId": A string defining the detector identifier. If not defined a unique indentifier will be generated, automatically. Since scdetect implements hierarchical logging specifying the detector identifier may be of particular use while debugging.

• "maximumLatency": The maximum data latency in seconds tolerated with regards to NOW. If data arrive later than the value specified it is not used, anymore. Note that data latency is not validated if scdetect is run in playback mode.

• "originId": Required. The origin identifier of the template origin the detector is referring to. The origin identifier is used for extracting template related data such as template waveforms, etc. Usually, the origin identifier corresponds to a seismic metadata resource identifier (smi). The relationship between a detector configuration and an origin is one-to-one.

• "streams": Required. An array of stream configuration JSON objects, also called a stream set. The stream set describes the streams to be covered by a detector. In a single-stream detector configuration the stream set contains just a single stream configuration, while a multi-stream detector configuration requires multiple stream configurations.

Gap interpolation:

• "gapInterpolation": A boolean value which enables/disables gap interpolation which allows interpolating gaps linearly.

• "gapThreshold": Threshold in seconds to recognize a gap.

• "gapTolerance": Maximum gap length in seconds to tolerate and to be handled.

Detections and arrivals:

• "arrivalOffsetThreshold": Maximum arrival offset in seconds (i.e. with regards to the template arrival) to tolerate when associating an arrival with an event. Note that the threshold is only relevant for a multi-stream detector setup.

• "createArrivals": A boolean value which defines if detections should include detected arrivals, i.e. arrivals with regards to the streams included within the stream set. If enabled, origins will be created with detected arrivals being associated, else origins are created not containing any reference to detected arrivals. In a multi-stream detector configuration setup detections will include only arrivals of those streams which contributed. For further details, please refer to "createTemplateArrivals" and "minimumArrivals" configuration parameters.

• "createTemplateArrivals": A boolean value which defines if detections should include so called template arrivals. Template arrivals refer to streams which are not part of the detector configuration's stream set, but contain valid picks as part of the template origin.

• "minimumArrivals": Defines the minimum number of arrivals w.r.t. streams within the stream set configured which must be part of an event to qualify for a detection.

• "timeCorrection": Defines the time correction in seconds for both detections and arrivals. That is, this allows shifting a detection in time.

Trigger facilities:

An event is considered as a detected event, also called a detection if it surpasses the value specified by the "triggerOnThreshold" configuration parameter.

In a multi-stream detector setup, scdetect uses the mean correlation coefficient of all streams within the stream set. In future, further methods may be provided in order to compute this score.

Besides, scdetect implements trigger facilities, i.e. a detected event may not be published, immediately, but put on-hold for the duration defined by the value of the "triggerDuration" configuration parameter. If a better detected event arrives within this period, the previous one is not used, anymore.

• "triggerDuration": Defines the trigger duration in seconds. A negative value disables triggering facilities.

• "triggerOnThreshold": Defines the threshold ([-1, 1]) to trigger the detector.

• "triggerOffThreshold": Defines the lower threshold ([-1, 1]) to emit a detection once the detector is triggered. Note that the configured value is only taken into account if trigger facilities are enabled.

Stream configuration parameters

A stream set must contain at least a single stream configuration. For a multi-stream detector setup multiple stream configurations may be provided. A stream configuration JSON object allows setting the following template specific configuration parameters:

General:

• "templateId": A string defining the stream related template identifier. If undefined a unique indentifier will be generated, automatically. Since scdetect implements hierarchical logging specifying the template identifier may be of particular use while debugging.

• "waveformId": Required. A string defining the waveform stream identifier of the stream to be processed. Usually, this refers to a FDSN Source Identifier. Note that the string is parsed and matched against NET, STA, LOC, CHA codes.

Template waveform:

• "templateWaveformId": A string defining an alternative waveform stream identifier referring to the stream used for the template waveform creation. If not defined, the template waveform is created from the stream specified by the "waveformId" configuration parameter. While for the phase code lookup the sensor location is used (i.e. the CHA component of the waveform stream identifier is neglected) for template waveform creation all waveform stream identifier components are taken into account.

• "templatePhase": Required. A string defining the template phase code used for the template waveform creation. Note that for the template phase lookup, only the sensor location related part is used of waveform stream identifier configured.

• "templateWaveformStart": The template waveform start in seconds with regards to the template pick time. A negative value refers to a template waveform start before the template pick time, while a positive value means after the pick time.

• "templateWaveformEnd": The template waveform end in seconds with regards to the template pick time. A negative value refers to a template waveform start before the template pick time, while a positive value means after the pick time.

Filtering and resampling:

• "initTime": The initialization time in seconds for that the stream related processor is blind after initialization. Setting this configuration parameter allows taking filter related artifacts during initialization into account.

• "filter": A string defining the filter to be applied to the processed stream. The filter must be specified following the SeisComP's filter grammar syntax. Filtering may be disabled by means of explicitly defining the empty string i.e. "". By default, the filter associated with the template pick is applied.

• "templateFilter": A string defining the filter during the template waveform generation. For further information, please refer to the description of the "filter" configuration property.

• "targetSamplingFrequency": Optionally, defines the target sampling frequency. Both the template waveform and the stream to be processed may be required to be resampled to the sampling frequency specified. Note that data is resampled before being filtered.

Stream configuration defaults

The following stream configuration default parameters may be defined within the scope of a detector configuration:

• "filter"
• "initTime"
• "targetSamplingFrequency"
• "templateFilter"
• "templatePhase"
• "templateWaveformStart"
• "templateWaveformEnd"

That is, if not explictly overridden by stream configurations the corresponding fallback values will be used.

Example:

    {
        "detectorId": "detector-01",
        "createArrivals": true,
        "createTemplateArrivals": true,
        "gapInterpolation": true,
        "gapThreshold": 0.1,
        "gapTolerance": 1.5,
        "triggerDuration": -1,
        "triggerOnThreshold": 0.98,
        "triggerOffThreshold": 0,
        "originId": "smi:ch.ethz.sed/sc3a/origin/NLL.20201026144442.91156.194937",
        "templatePhase": "Pg",
        "filter": "",
        "templateFilter": "",
        "initTime": 0,
        "streams": [
              {
                  "templateId": "template-01",
                  "templateWaveformStart": -2,
                  "templateWaveformEnd": 2,
                  "waveformId": "CH.GRIMS..HHZ",
                  "templateWaveformId": "CH.GRIMS..HHZ",
              },
              {
                  "templateId": "template-02",
                  "templateWaveformStart": -3,
                  "templateWaveformEnd": 1,
                  "waveformId": "CH.HASLI..HHZ",
                  "templateWaveformId": "CH.HASLI..HHZ",
                  "templatePhase": "Sg"
              }
        ]
    }

In the example above, the stream configuration default "templatePhase" is used indicating a default phase code "Pg". While this stream configuration default value is used by the stream configuration object identified by the template identifier "template-01", it is overridden by the stream configuration identified by "template-02" (i.e. it uses "Sg" instead).

Besides, filtering is explicitly disabled for all stream configurations within the stream set.

Inventory, events and configuration

SeisComP stores and reads certain data (e.g. inventory, eventparameters, etc.) in and from a database. In order to connect to the database a database connection URL is required. This URL is either configured in global.cfg or in scmaster.cfg (i.e. the configuration file of SeisComP's messaging mediator module, scmaster). In the latter case, it is the scmaster module that passes the database connection URL to every module connecting to the messaging system (usually at module startup).

However, when running scdetect in offline mode (using the CLI option --offline), and the database connection URL is specified in scmaster.cfg, scdetect does not connect to the messaging system and thus, the database connection URL never reaches scdetect. For this purpose scdetect provides the standard SeisComP CLI options:

• -d|--database URL
• --inventory-db URI
• --config-db URI

The non-standard --event-db URI option allows reading eventparameter related data from either a file or a database specified by URI (Note that the --event-db URI CLI option overrides the -d|--database URL CLI option.). With that, both inventory metadata and eventparameters might be read from plain files, making the database connection fully optional. E.g.

$ ls -1
catalog.scml
data.mseed
inventory.scml
templates.json
$ scdetect \
  --templates-json templates.json \
  --inventory-db file://$(realpath inventory.scml) \
  --event-db file://$(realpath catalog.scml) \
  -I file://$(realpath data.mseed) \
  --offline \
  --ep=detections.scml

In the example above even the waveform data is read from a file (i.e. data.mseed). Furthermore, the resulting detections are dumped SCML formatted to the detections.scml file.

Note that as the --config-db URI CLI option is a standard SeisComP module CLI option it is mentioned for completeness, only. Since scdetect does not support station bindings, anyway, this CLI can be neglected.

Waveform data and RecordStream configuration

SeisComP applications access waveform data through the RecordStream interface. It is usually configured in global.cfg, where the user is able to define the backend services in order to access either real-time and/or historical waveform data. A technical documentation including exemplary RecordStream configurations can be found here.

Alternatively, the RecordStream can be defined making use of scdetect's -I [ --record-url ] URI CLI flag (Note that this is the standard CLI flag used for all SeisComP modules implementing SeisComP's StreamApplication interface.).

In general, with regards to waveform data scdetect implements the following approach:

1. Initialization: Download template waveform data from the archive RecordStream specified. Cache the raw waveform data (see Caching waveform data) and filter the template waveforms according to the configuration.

2. Processing: Start processing the waveform data from either the real-time or the archive RecordStream configured.

Caching waveform data

Unless the RecordStream points to a local disk storage, downloading waveforms might require a lot of time. For this reason scdetect stores raw template waveform data on disk after downloading them. The cache is located under ${SEISCOMP_ROOT}/var/cache/scdetect. If omitting cached waveform data is desired, make use of scdetect's --templates-reload CLI flag.

In order to remove cached waveform data, simply invoke

$ rm -rvf ${SEISCOMP_ROOT}/var/cache/scdetect

Prepare template waveform data

Although, SeisComP allows configuring a combined RecordStream, sometimes it might be useful to fetch template waveform data from a different RecordStream than the RecordStream providing the data being processed. For this purpose, scdetect provides the --templates-prepare CLI flag. With that, an exemplary processing workflow might look like:

$ scdetect \
  --templates-json path/to/templates.json \
  --inventory-db file:///absolute/path/to/inventory.scml \
  --event-db file:///absolute/path/to/catalog.scml \
  --record-url fdsnws://eida-federator.ethz.ch/fdsnws/dataselect/1/query \
  --offline \
  --templates-prepare

I.e. template waveform data is downloaded from the FDSNWS RecordStream specified by fdsnws://eida-federator.ethz.ch/fdsnws/dataselect/1/query. After initializing the module returns.

Next, run the module for processing, but now use the previously cached template waveform data when loading template waveforms, e.g.

$ scdetect \
  --templates-json path/to/templates.json \
  --inventory-db file:///absolute/path/to/inventory.scml \
  --event-db file:///absolute/path/to/catalog.scml \
  --record-url "slink://localhost:18000?timeout=60&retries=5" \
  --offline \
  --ep=detections.scml

Compiling and Installation

Get a copy of SeisComP/seiscomp:

$ git clone https://github.com/SeisComP/seiscomp.git && cd seiscomp/src/extras/

Next, clone scdetect:

$ git clone https://github.com/damb/scdetect.git

Dependencies:

Besides of the SeisComP core dependencies the following packages must be installed to compile scdetect:

• libsqlite3-dev (Debian, Ubuntu), sqlite-devel (RedHat, Fedora, CentOS), dev-db/sqlite (Gentoo)

For compiling SeisComP (including scdetect), please refer to https://github.com/SeisComP/seiscomp#build.

Tests

In order to run all SeisComP tests (including those of scdetect and possibly additionally installed third party modules), either execute

$ make test

in the build directory, or use the ctest executable from cmake (also within the build directory). E.g. in order to run only scdetect related tests, invoke

$ ctest -R "^test_scdetect.*"

For additional information, please also refer to SeisComP's unit testing guide.

Issues

Please report bugs, issues, feature requests, etc on GitHub.

Contributions

Contributions are very welcome. Made with 💕.

License

Licensed under the the AGPLv3. For more information see the LICENSE file.