Timing problem at Mammoth analog stations 01/22/2015 - 01/27/2015

January 30th, 2015

January 30th, 2015

The Northern California Earthquake Data Center (NCEDC) archives seismic waveform data from the Northern California Seismic Network (network code NC). This announcement refers to network NC seismic waveform data (both continuously archived data and event gathers) for dates, stations, and channels listed below. Earthquake catalog locations were not affected (see below).

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The NCSN experienced problems with the TrueTime clock responsible for providing the IRIGE time at Mammoth from 01/22/2015 23:35:11 through 01/27/2015 23:59:12. During this interval, timing is uncertain for all the analog stations digitized at Mammoth. However, events recorded during this period were timed and located with stations not affected by the problem, and the origin times of the cataloged events are accurate, with fairly good locations.

Beginning of problem - time tears from lost/regained time lock, presumably due to TrueTime IRIGE changes:


20150121_UTC_23:35:11 overlap -0.99 s
20150122_UTC_01:02:58 gap 1.01 s
20150122_UTC_06:02:31 overlap -0.99 s
20150122_UTC_06:40:09 gap 1.01 s
20150122_UTC_07:30:11 overlap -0.99 s


End of problem - TrueTime swap done, adsend synced:
20150127_UTC_23:59:12 Time-code status: Locked-on

Timing between 01:02:58-06:02:31 and 06:40:09-07:30:11 on 1/22 is probably ok.

This timing problem affects the following channels:

IRGMM ATT NC --
MCD EHZ NC --
MCS EHZ NC --
MCV EHZ NC --
MDC EHZ NC 02
MDR EHZ NC 02
MDR ELE NC --
MDR ELN NC --
MEM EHZ NC --
MEM ELE NC --
MEM ELN NC --
MFB EHZ NC --
MGPB EHZ NC --
MLC EHZ NC --
MLH EHZ NC --
MLM EHZ NC --
MMP EHZ NC --
MMS EHZ NC --
MRC EHZ NC --
MRD EHZ NC 02
MTU EHZ NC 02

EGS Catalog Geysers Magnitude Errors

January 3rd, 2015

January 3rd, 2015

The Northern California Earthquake Data Center hosts several earthquake catalogs, including the the northern California earthquake catalogs of the USGS and BSL, the worldwide earthquake catalog of the ANSS, and the Enhanced Geothermal Systems (EGS) catalog. Below please see an announcement regarding magnitude errors for four Geysers-area earthquakes in the EGS catalog:

In reviewing Geysers data, the 4 events listed below had incorrect amplitudes from one station (DEB) that had a large amount of transient electronic noise. These amplitudes were previously included in the moment magnitude calculations for the events listed below, resulting in greatly exaggerated moment magnitude estimates. The corrected magnitude estimates, computed without the erroneous DEB amplitudes, are:

Date       Time              Lat        Lon   Depth   Mag Magt  Nst Gap  Clo  RMS  SRC   Event ID
----------------------------------------------------------------------------------------------
2014/04/05 19:30:20.53  38.84790 -122.83538   2.543 0.43 (formerly 4.92)  ML    0   0    0 0.05  LBL    3383465
2014/04/05 19:52:57.37  38.84423 -122.82652   2.857 1.12 (formerly 4.87)  ML    0   0    0 0.01  LBL    3383466
2014/04/05 20:04:52.30  38.80133 -122.82338   1.035 0.45 (formerly 5.06)  ML    0   0    0 0.03  LBL    3383470
2014/04/07 01:18:36.17  38.83748 -122.78598   0.851 0.51 (formerly 4.65)  ML    0   0    0 0.04  LBL    3383663
---------------------------------------------------------------------------------------------- 

EventData Web Service for Event-Associated MiniSEED Time Series

June 30th, 2014

June 30th, 2014

The NCEDC is pleased to announce a new NCEDC web service for retrieving event-associated time series from the NCEDC. Web services provide simple functions that can be used from a web browser, command-line programs such as curl and wget, dedicated clients, and through programming languages such as perl, python, shell scripts, or MATLAB.

ncedc-eventdata
The ncedc-eventdata web service returns miniSEED time series data for the specified event from the specified earthquake catalog. In it simplest form, it returns the time series for all channels and time intervals that have been associated with the event at the NCEDC. This web services provides a functional replacement for the email-base EVT-FAST service.

The NCEDC currently supports 2 event catalogs for event-associated time series events: the NCSS and the EGS catalogs.

Using the GET method, you can optionally restrict which data channels to retrieve by specifying a (wildcarded) selection of SEED Network, Station, Location, and Channel names, and an optional start time and end time for the time series. Using the POST method, you can specify a list of (wildcarded) channel names, a global restricted time window, and specific restricted time window for each specified channel. Each ncedc-eventdata web service request can only request data for a single event. You can easily generate and submit ncedc-eventdata requests using command line programs such as wget, curl, MATLAB, or dedicated client programs provided by the NCEDC.

Client programs for the ncedc-eventdata web service
FetchEventData
The program FetchEventData is a command-line fetch script that uses the ncedc-eventdata service to event-associated time series for the specified eventid from the specified catalog. Its command-line options provide support for all of the ncedc-eventdata selection options.

mssplit
The program mssplit is used to split a stream of MiniSEED records into a separate file for each data channel. It can optionally create a new directory for these data files. It can read data from either from a file or from stdin.

Examples

FetchEventData -E 72099881 -C NCSS | mssplit -D NCSS.72099881

Will retrieve all time series data for the eventid 72099881 in the NCSS catalog, create a directory named NCSS.72099881, and save each data channel in a file named with the station, network, channel, location, and start time in the specified directory.

FetchEventData -E 72099881 -C NCSS -o msfile ; mssplit -D NCSS.72099881 msfile 

Will retrieve all time series data for the eventid 72099881 in the NCSS catalog, saving all data channels info a file name msfile. The mssplit program then splits the specified MiniSEED file into separate channel files in the specified directory.

The mssplit program can be used to split any multi-channel MINISeed file, such as those retrieved using FetchData or FetchData-ncedc.

Why web services?
Web services at the NCEDC use a RESTful (Representational State Transfer) design to provide a simple stateless query and data retrieval system. RESTful Web services use the HTTP protocol and normally communicate with clients using TCP port 80, which is the default port used by web servers. Using HTTP and standard web server ports minimizes interference from firewalls, and allows you to use web services anywhere you can use a web browser -- from behind most firewalls, and through web proxies.

Please visit the NCEDC Web Services Web Page for a complete list of NCEDC Web services and descriptions.

Double Difference Locations Now Available

June 2nd, 2014

June 2nd, 2014

The NCEDC is pleased to announce the availability of double difference (DD) hypocenter solutions from 1984 to the present for earthquakes recorded by the Northern California Seismic System (NCSS). The NCSS catalog can be searched via http://www.ncedc.org/ncedc/catalog-search.html by selecting "NCSS Double-Difference Catalog (1984-Present)" from the "Input Catalog" drop-down box at the top of the web page. Generation, archiving, and searching of the DD catalog at the NCEDC is made possible through the efforts of Felix Waldhauser, Pete Lombard, Stephane Zuzlewski, Paul Friberg, and Allan Walter.

The NCSS double-difference catalog is generated by 2 separate processes. The "base" catalog was computed at the Lamont-Doherty Earth Observatory (LDEO) by Felix Waldhauser and David Schaff from a simultaneous re-analysis of 27 years (1984-2011) of digital waveforms available at the NCEDC. Waveform cross correlation (CC) and DD methods are used to improve the resolution in the existing Hypoinverse earthquake catalog by up to three orders of magnitude. The base catalog is based on 1.7 billion CC differential time measurements with correlation coefficients, Cf>=0.7 from all correlated pairs of events that are separated by less than 5 km (Schaff and Waldhauser, 2005). These data, combined with 11.4 million P arrival times from the NCSS catalog, were inverted for the precise relative locations of 512,059 events using the hypoDD algorithm (Waldhauser and Schaff, 2008). Information on the base catalog is available at http://www.ldeo.columbia.edu/~felixw/NCAeqDD.

The "real-time" catalog is computed automatically using the Real Time Double Difference (DD-RT) method (Waldhauser, 2009). The DD-RT process relocates new earthquakes relative to the DD base catalog by using differential times between the new event and its neighboring (reference) events in the base catalog. Information on DD-RT is available http://ddrt.ldeo.columbia.edu. The Northern California DD-RT catalog also continues to be computed in near real-time at LDEO and made available at http:/ddrt.ldeo.columbia.edu. While the base catalogs at the NCEDC and LDEO are identical, the DD-RT solutions computed by the NCSS and LDEO systems are not guaranteed to be identical due to differences in computing environments and when waveforms are retrieved by the two systems. Tests indicate that the differences between solutions computed by the two DD-RT systems are below the noise level, with standard deviations of a few tens of meters/several milliseconds.

Users should understand the following limitations and caveats when using the DD catalog.

  • The base catalog will be periodically updated, resulting in a complete replacement of the entire DD catalog. Information on updates will be posted to the NCEDC blog and on the Lamont DDRT server at http://ddrt.ldeo.columbia.edu when that occurs.
  • It is not possible to compute a DD solution for every earthquake location in the NCEDC catalog. Users requiring the most complete catalog should select the "USGS NCSN Catalog (1967 - Present)" instead of the DD catalog.
  • The magnitudes reported with the DD catalog are identical to those reported in the "USGS NCSN Catalog (1967 - Present)". For most cases the small differences in hypocenter coordinates resulting from the DD method are unlikely to appreciably change event magnitudes. However, for poorly constrained earthquakes (e.g., offshore earthquakes), the DD hypocenters can differ by several kilometers from the NCSN catalog, and in such cases the reported magnitude is unreliable.
  • DD solutions have not been computed prior to 1984, as there are no digital waveforms available. We are considering computing solutions from only P arrival time data before 1984.
  • DD solutions are not reviewed by data analysts. Consequently, the status is set to "A" (automatic), even though the Hypoinverse solution is marked as "F" (finalized).
  • For users selecting the "Hypoinverse" output format, note that the following hypocenter solution values have no corresponding values in the DD catalog
    • Number of P & S times with final weights greater than 0.1.
    • Maximum azimuthal gap, degrees.
    • Distance to nearest station (km).
    • RMS travel time residual.
    • Azimuth of largest principal error (deg E of N).
    • Dip of largest principal error (deg).
    • Size of largest principal error (km).
    • Azimuth of intermediate principal error.
    • Dip of intermediate principal error.
    • Size of intermediate principal error (km).
    • Size of smallest principal error (km).
    • Number of S times with weights greater than 0.1.
  • The following error estimates are available:
    • Bootstrap relative location errors at the 95% confidence level (base catalog).
    • Formal least-squares errors at the 95% confidence level (real-time catalog).

References

Schaff, D.P. and F. Waldhauser, Waveform Cross-Correlation-Based Differential Travel-Time Measurements at the Northern California Seismic Network, Bull. Seism. Soc. Am., 95, 2446-2461, 2005.
Waldhauser, F. and D.P. Schaff, Large-scale relocation of two decades of Northern California seismicity using cross-correlation and double-difference methods, J. Geophys. Res.,113, B08311, doi:10.1029/2007JB005479, 2008.
Waldhauser, F., Near-real-time double-difference event location using long-term seismic archives, with application to Northern California, Bull. Seism. Soc. Am., 99, 2736-2848, doi:10.1785/0120080294, 2009.

The NCEDC is a joint project of the University of California, Berkeley and the USGS, with facilities located at the University of California, Berkeley. Please send us email at ncedcinfo {AT} ncedc {DOT} org or fill out our comments form if you have questions or comments about these changes.

New NCEDC Web Services and Web Service Home

July 19th, 2013

July 19th, 2013

The NCEDC is pleased to announce a new home for the NCEDC web services and a new set of FDSN-compliant web services to access data at the NCEDC. Web services provide simple functions that can be used from a web browser, command-line programs such as curl and wget, dedicated clients, and through programming languages such as perl, python, shell scripts, or MATLAB.

New NCEDC Web Service Home:
In order to provide better service, all NCEDC web services can now be found at the new site
http://service.ncedc.org/

FDSN web services:
The NCEDC is introducing new FDSN-compliant web services. The FDSN web services provide a common specificiation to access common FDSN data types such as event information, station and information, and waveform data. The FDSN web services specification serves as a baseline level of compatibility, allowing data request tools to work with any FDSN data center that implementing these services.

The NCEDC has implemented the following FDSN web services:

fdsnws-dataselect
The fdsnws-dataselect web service returns multiple channels of FDSN miniSEED data for specified time ranges specified time ranges. With this service you specify a list of selections composed of network, station, location, channel, start-time and end-time and the service streams back the selected raw waveform data. fdsnws-dataslect can handle large selections and can be easily driven by command line programs such as wget, curl or dedicated client programs.

fdsnws-event
The fdsnws-event web service returns event information for a specified time and regions. Event info can include basic event information such as time, hypocenter, and magnitude, or more complete information that includes phase data. NCEDC-specific enhancements can also provide mechanism and moment tensor information. fdsnws-event can handle large selections and can be easily driven by command line programs such as wget, curl or dedicated client programs.

fdsnws-station
The fdsnws-station web service returns station and channel information for requested stations and channels The data is returned in FDSN StationXML format. fdsnws-station can handle large selections and can be easily driven by command line programs such as wget, curl or dedicated client programs.

Why web services?
Web services at the NCEDC use a RESTful (Representational State Transfer) design to provide a simple stateless query and data retrieval system. RESTful Web services use the HTTP protocol and normally communicate with clients using TCP port 80, which is the default port used by web servers. Using HTTP and standard web server ports minimizes interference from firewalls, and allows you to use web services anywhere you can use a web browser -- from behind most firewalls, and through web proxies.

The NCEDC FDSN web services are designed to be compatible with the FDSN web services implemented at other FDSN data centers such as the IRIS DMC Web Services. named web services at the IRIS DMC. Please visit the NCEDC Web Services Web Page for a complete list of NCEDC Web services and descriptions.


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