Stabilize the computation of derivatives in the Okal geometrical spre…

…ading model
SeismicSource · Dec 18, 2024 · e826283 · e826283
1 parent 6484778
commit e826283
Show file tree

Hide file tree

Showing 2 changed files with 4 additions and 1 deletion.
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -51,6 +51,8 @@ Copyright (c) 2011-2024 Claudio Satriano <satriano@ipgp.fr>
   USGS) where the phase name is not in the `<phase_hint>` attribute of the
   `<pick>` element but in the `<phase>` attribute of the corresponding
   `<arrival>` element
+- Stabilize the computation of derivatives in the Okal geometrical spreading
+  model, thus avoiding numerical instabilities.
 
 ## v1.8 - 2024-04-07
 

diff --git a/sourcespec/ssp_util.py b/sourcespec/ssp_util.py
@@ -398,7 +398,8 @@ def geom_spread_teleseismic(
     # angular distance (dd, also called the aperture of the ray tube).
     # We use a finite difference approximation, and we increase the aperture
     # until we get a non-zero value.
-    aperture = 0.1  # degrees
+    # As a first guess, we set the aperture to half the angular distance
+    aperture = angular_distance/2
     for _ in range(10):
         dtdd = _compute_dtdd(
             angular_distance, aperture, source_depth_in_km, phase_list)