catalog {ETAS}

Create an Earthquake Catalog

Description

Creates an object of class "catalog" representing an earthquake catalog dataset. An earthquake catalog is a chronologically ordered list of time, epicenter and magnitude of all recorded earthquakes in geographical region during a specific time period.

Usage

  catalog(data, time.begin=NULL, study.start=NULL,
          study.end=NULL, study.length=NULL,
          lat.range=NULL, long.range=NULL,
          region.poly=NULL, mag.threshold=NULL,
          flatmap=TRUE, dist.unit = "degree", 
          roundoff=TRUE, tz="GMT")
  

Arguments

data

A data.frame containing date, time, latitude, longitude and magnitude of earthquakes.

time.begin

The beginning of time span of the catalog. A character string or an object that can be converted to date-time (calendar dates plus time to the nearest second) by as.POSIXlt. The default NULL sets it to the date-time of the first event.

study.start

The start of the study period. A character string or an object that can be converted to date-time by as.POSIXlt. If not specified (NULL), then time.begin is used.

study.end

The end of the study period. A character string or an object that can be converted to date-time by as.POSIXlt. The default NULL sets it to the date-time of the last event.

study.length

A single numeric value specifying the length of the study period in decimal days. Incompatible with study.end: either study.end or study.length can be specified, but not both.

lat.range

The latitude range of a rectangular study region. A numeric vector of size 2 giving (latmin, latmax). By default (NULL) the range of the latitudes of events is used.

long.range

The longitude range of a rectangular study region. A numeric vector of size 2 giving (longmin, longmax). By default (NULL) the range of the longitudes of events is used.

region.poly

Polygonal boundary of a non-rectangular study region. A list with components lat and long of equal length specifying the coordinates of the vertices of a polygonal study region. The vertices must be listed in anticlockwise order.

mag.threshold

The magnitude threshold of the catalog. A positive numeric value. The default (NULL) sets it to the minimum magnitude of all events.

flatmap

Logical flag indicating whether to transform the spherical coordinates (long, lat) on the earth surface to flat map (planar) coordinates (x, y) in order to approximate the great-circle distance on the sphere by the corresponding Euclidean distance on the flat map.

dist.unit

A character string specifying the unit of geographical coordinates and spatial distances between events. Options are "degree" (the default case) and "km".

roundoff

Logical flag indicating whether to account for round-off error in coordinates of epicenters.

tz

A character string specifying the time zone to be used for the date-time conversion in as.POSIXlt. The default "GMT" is the UTC (Universal Time, Coordinated).

Details

The data is required to have at least 5 columns with names date, time, lat, long and mag containing, respectively, the date, time, latitude, longitude and magnitude of each event in the catalog.

The geographical study region can be rectangular or polygonal:

• rectangular study region can be specified by lat.range and long.range which must be numeric vectors of length 2.

• polygonal study region can be specified by region.poly which contains coordinates of the vertices of the polygon. It must be either a list with components lat and long of equal length or a data.frame with columns lat and long. The vertices must be listed in anticlockwise order and no vertex should be repeated (i.e. do not repeat the first vertex).

The function inside.owin in the spatstat is used to indicate whether events lie inside the study region. Only events inside the study region and the study period (study.start, study.end) are considered as target events. Other events are assumed to be complementary events.

If the events in data are not chronologically sorted, then a warning will be produced and the events will be sorted in ascending order with respect to time of occurrence.

If flatmap=TRUE, longitude-latitude coordinates convert to flat map coordinates:

• if dist.unit="degree", then the Equirectangular projection

  x = \cos(cnt.lat/180 \pi) (long - cnt.long)

  and y = lat - cnt.lat is used to obtain the flat map coordinates (x, y) in degrees, where cnt.lat and cnt.long are, respectively, the latitude and longitude of the centroid of the geographical region.

• if dist.unit="km", then the projection

  x = 111.32 \cos(lat/180 \pi) long

  and y = 110.547 lat is used where x and y are in (approximate) kilometers.

Value

An object of class "catalog" containing an earthquake catalog dataset.

Author(s)

Abdollah Jalilian [e-mail]

References

Zhuang J (2012). Long-term Earthquake Forecasts Based on the Epidemic-type Aftershock Sequence (ETAS) Model for Short-term Clustering. Research in Geophysics, 2(1), 52–57. doi:10.4081/rg.2012.e8.

See Also

etas.

Examples

  summary(iran.quakes)

  # creating a catalog with rectangular study region
  iran.cat <- catalog(iran.quakes, time.begin="1973/01/01",
     study.start="1985/01/01", study.end="2016/01/01",
     lat.range=c(25, 42), long.range=c(42, 63),
     mag.threshold=4.5)

  print(iran.cat)
  ## Not run: 
  plot(iran.cat)
  
## End(Not run)

  # equivalently, specifying the length of the study period
  iran.cat2 <- catalog(iran.quakes, time.begin="1973/01/01",
     study.start="1985/01/01", study.length=11322,
     lat.range=c(25, 42), long.range=c(42, 63),
     mag.threshold=4.5)

  print(iran.cat2)


  # specifying a polygonal geographical region
  jpoly <- list(long=c(134.0, 137.9, 143.1, 144.9, 147.8,
      137.8, 137.4, 135.1, 130.6), lat=c(31.9, 33.0, 33.2,
      35.2, 41.3, 44.2, 40.2, 38.0, 35.4))
  # creating a catalog with polygonal study region
  japan.cat <- catalog(japan.quakes, time.begin="1966-01-01",
      study.start="1970-01-01", study.end="2010-01-01",
      region.poly=jpoly, mag.threshold=4.5)

  print(japan.cat)
  ## Not run: 
  plot(japan.cat)
  
## End(Not run)