Added new dynamic strain scaling

DESCRIPTION

@@ -1,8 +1,8 @@
 Package: deform
 Type: Package
-Title: Crustal deformation modeling tools in R
-Version: 0.0.999
-Date: 2019-07-12
+Title: Crustal Deformation Modeling Tools in R
+Version: 0.0.989
+Date: 2020-06-19
 Author: Andrew J. Barbour; some of these tools were
     adapted from Matlab(tm) codes by Brendan Crowell (UW),
     and Francois Beauducel (IPGP).
@@ -12,6 +12,7 @@ Description: Crustal deformation modeling tools.  Currently this
     depleting reservoirs (i.e., Geertsma, 1973; Segall, 1985, 1989, 1992),
     spherical cavities (i.e., Mogi, 1958), and
     injection point-source (i.e., Rudnicki, 1986).
+    One can also calculate strains from Mag-Dist relationships.
 License: GPL
 Imports:
     Rcpp (>= 0.11.2),
@@ -32,5 +33,5 @@ Suggests:
     testthat,
     covr
 LinkingTo: Rcpp
-RoxygenNote: 6.1.1
+RoxygenNote: 7.1.0
 Encoding: UTF-8

R/strain_magdist_scaling.R

@@ -1,14 +1,54 @@
 #' Predict the level of strain expected for magnitude and distance
+#' 
+#' @details 
+#' Currently the options for \code{model} are:
+#' \describe{
+#'   \item{\code{'static'}}{Static RMS strain from an earthquake (Wyatt, 1988)}
+#'   \item{\code{'dynamic'}}{Dynamic RMS strain from a seismic wave:
+#'   \code{'aw14'} for Agnew and Wyatt (2014): applicable to teleseisms at thousands of km (inaccurate within 500km or so); or
+#'   \code{'bc17'} for Barbour and Crowell (2017): applicable to regional earthquakes at < 500 km (inaccurate
+#'   for very short distances); or
+#'   \code{'fbl20'} for Farghal, Barbour and Langbein (2020): applicable to regional earthquakes 
+#'   at < 500 km (best accuracy at short distances; inaccurate > 500 km);
+#'   }
+#' }
 #' @name magnitude-distance
 #' @param Mw numeric; the moment magnitude of the earthquake
 #' @param Distance.km numeric; the epicentral distance, in kilometers
 #' @param km2deg numeric; specify the scaling coefficient used to
 #' convert the distance (in km) to degrees; this may be useful if,
 #' for example, the distance is already in degrees (then set it equal to 1)
-#' @param model character; the strain-scaling model to use; currently ignored
-#' because there are no alternatives
+#' @param model character; the strain-scaling model to use (see Details)
 #' @param strn.type character; the type of strain-scaling relationship to
 #' provide a prediction for
+#' 
+#' @references Agnew, D. C., and F. K. Wyatt (2014),
+#' Dynamic strains from regional and teleseismic earthquakes, 
+#' Bull. Seismol. Soc. Am. 104, no. 4, 1846– 1859, 
+#' doi: 10.1785/0120140007
+#' 
+#' @references Barbour, A., and B. Crowell (2017),
+#' Dynamic strains for earthquake source characterization, 
+#' Seismol. Res. Lett. 88, no. 2A, 354–370, 
+#' doi: 10.1785/0220160155
+#' 
+#' @references Farghal, N., A. Barbour, and J. Langbein (2020),
+#' The Potential of Using Dynamic Strains in Earthquake Early Warning Applications, 
+#' Seismol. Res. Lett., in press, 1–12, 
+#' doi: 10.1785/0220190385
+#' 
+#' @references Wyatt, F. K. (1988),
+#' Measurements of coseismic deformation in southern California: 1972–1982, 
+#' J. Geophys. Res. 93, no. B7, 7923–7942, 
+#' doi: 10.1029/JB093iB07p07923
+#' 
+#' @examples 
+#' static(7.2, 220)
+#' dynamic(7.2, 15000, model='aw14')
+#' 
+#' dynamic(7.2, 150, model='aw14')
+#' dynamic(7.2, 150, model='bc17')
+#' dynamic(7.2, 150, model='fbl20')
 NULL
 
 #' @rdname magnitude-distance
@@ -20,33 +60,56 @@ static <- function(Mw, Distance.km, model="w88"){
 
 #' @rdname magnitude-distance
 #' @export
-dynamic <- function(Mw, Distance.km, km2deg=NULL, model="aw14",
-                    strn.type=c('general','areal','diffext','shear','dil')){
+dynamic <- function(Mw, Distance.km, model=c("aw14",'bc17','fbl20'),
+                    strn.type=c('general','areal','diffext','shear','dil'),
+                    km2deg=NULL){
+
+  model <- match.arg(model)
+  Distance <- Distance.km
+
   if (is.null(km2deg)){
     km2deg <- 1/111.3195
   }
-  Distance.deg <- Distance.km * km2deg
-  ld <- log10(Distance.deg)
-  strn.type <- match.arg(strn.type)
-  lstrn <- if (strn.type %in% c("areal",'diffext')){
-    # areal or differential extension
-    Err <- 10**(0.93*Mw - 1.63*ld - 2.66)
-    Ett <- 10**(0.86*Mw - 1.73*ld - 2.46)
-    strn <- if (strn.type=="areal"){
-      Ett + Err
+  if (model %in% c('aw14')){
+    Distance <- Distance * km2deg
+  }
+
+  ld <- log10(Distance)
+
+  lstrn <- if (model == 'fbl20'){
+    # Farghal, Barbour and Langbein (2020) Equation 11
+    0.83*Mw - 1.43*ld - 0.0013 * Distance - 8.051
+  } else if (model == 'bc17'){
+    # Barbour and Crowell (2017) Equation 8
+    1.25*Mw - 1.992*ld - 9.513
+  } else if (model == 'aw14'){
+    # Agnew and Wyatt (2014)
+    strn.type <- match.arg(strn.type)
+    LS <- if (strn.type %in% c("areal",'diffext')){
+      # areal or differential extension
+      Err <- 10**(0.93*Mw - 1.63*ld - 2.66)
+      Ett <- 10**(0.86*Mw - 1.73*ld - 2.46)
+      strn <- if (strn.type=="areal"){
+        Ett + Err
+      } else {
+        Ett - Err
+      }
+      log10(strn)
+    } else if (strn.type=="shear"){
+      # shear
+      0.92*Mw - 1.77*ld - 2.64
+    } else if (strn.type=="dil"){
+      # dilatation
+      0.94*Mw - 1.64*ld - 2.88
     } else {
-      Ett - Err
+      # general relation
+      0.95*Mw - 1.65*ld - 2.8
     }
-    log10(strn)
-  } else if (strn.type=="shear"){
-    # shear
-    0.92*Mw - 1.77*ld - 2.64
-  } else if (strn.type=="dil"){
-    # dilatation
-    0.94*Mw - 1.64*ld - 2.88
+    # they report in nanostrain, so correct to unscaled strain
+    LS - 9
   } else {
-    # general relation
-    0.95*Mw - 1.65*ld - 2.8
+    stop('bad model specification')
   }
-  return(lstrn - 9)
+
+  return(lstrn)
 }