Cake manual¶
Cake is a tool which can be used to solve classical seismic ray theory problems for layered earth models (layer cake models).
For various seismic phases it can calculate:
 arrival times
 ray paths
 reflection and transmission coefficients
 takeoff and incidence angles
 geometrical spreading factors
Computations are done for a spherical earth. Cake can either be run as a command line tool or used as a Python module. Both is demonstrated in the examples below.
Invocation¶
cake <subcommand> [options]
Subcommands:

print
get information on model/phase/material properties

arrivals
print list of phase arrivals

paths
print ray path details

plotxt
plot traveltime vs distance curves

plotxp
plot ray parameter vs distance curves

plotrays
plot ray propagation paths

plot
plot combination of ray and traveltime curves

plotmodel
plot velocity model

listmodels
list builtin velocity models

listphasemap
show translation table for classic phase names

simplifymodel
create a simplified version of a layered model

scatter
show details about scattering at model interfaces
To get further help and a list of available options for any subcommand run:
cake <subcommand> help
Options¶
Each subcommand has its own set of options. Use cake <subcommand> help
to
see which of the following options apply to any of the subcommands listed
above.
Phases:¶
Seismic phase arrivals may be either specified as traditional phase names
(e.g. P, S, PP, PcP, …) or in Cake’s own syntax which is more powerful.
Use the classic
option, for traditional phase names. Use the phase
option if you want to define phases in Cake’s syntax.

phase
=PHASE1,PHASE2,...
,
phases
=PHASE1,PHASE2,...
¶ Comma separated list of seismic phases in Cake’s syntax.
The definition of a seismic propagation path in Cake’s phase syntax is a string consisting of an alternating sequence of legs and knees.
A leg represents seismic wave propagation without any conversions, encountering only supercritical reflections. Legs are denoted by
P
,p
,S
, ors
. The capital letters are used when the takeoff of the leg is in a downward direction, while the lower case letters indicate a takeoff in an upward direction.A knee is an interaction with an interface. It can be a mode conversion, a reflection, or propagation as a headwave or diffracted wave.
 conversion is simply denoted as:
(INTERFACE)
orDEPTH
 upperside reflection:
v(INTERFACE)
orvDEPTH
 underside reflection:
^(INTERFACE)
or^DEPTH
 normal kind headwave or diffracted wave:
v_(INTERFACE)
orv_DEPTH
The interface may be given by name or by depth: INTERFACE is the name of an interface defined in the model, DEPTH is the depth of an interface in [km] (the interface closest to that depth is chosen). If two legs appear consecutively without an explicit knee, surface interaction is assumed.
The preferred standard interface names in cake are
conrad
,moho
,cmb
(coremantle boundary), andicb
(inner core boundary).The phase definition may end with a backslash
\
, to indicate that the ray should arrive at the receiver from above instead of from below. It is possible to restrict the maximum and minimum depth of a leg by appending<(INTERFACE)
or<DEPTH
or>(INTERFACE)
or>DEPTH
after the leg character, respectively. conversion is simply denoted as:

classic
=PHASE1,PHASE2,...
¶ Comma separated list of seismic phases in classic nomenclature. Run
cake listphasemap
for a list of available phase names.
Model:¶

model
=(NAME or FILENAME)
¶ Use builtin model named NAME or user model from file FILENAME. By default, the “ak135fcontinental.m” model is used. Run
cake listmodels
for a list of builtin models.

format
=FORMAT
¶ Set model file format (available: nd, hyposat; default: nd).

crust2loc
=LAT,LON
¶ Set model from CRUST2.0 profile at location (LAT,LON).
Sourcereceiver geometry:¶

sdepth
=FLOAT
¶ Source depth [km] (default: 0)

rdepth
=FLOAT
¶ Receiver depth [km] (default: 0)

distances
=DISTANCES
¶ Surface distances as
start:stop:n
ordist1,dist2,...
[km]
Material:¶
An isotropic elastic material may be specified by giving a combination of some of the following options.

vp
=FLOAT
¶ Pwave velocity [km/s]

vs
=FLOAT
¶ Swave velocity [km/s]

rho
=FLOAT
¶ density [g/cm**3]

qp
=FLOAT
¶ Pwave attenuation Qp (default: 1456)

qs
=FLOAT
¶ Swave attenuation Qs (default: 600)

poisson
=FLOAT
¶ Poisson ratio

lambda
=FLOAT
¶ Lame parameter lambda [GPa]

mu
=FLOAT
¶ Shear modulus [GPa]

qk
=FLOAT
¶ Bulk attenuation Qk

qmu
=FLOAT
¶ Shear attenuation Qmu
General:¶

h
,
help
¶
Show help message and exit.

vred
=FLOAT
¶ Velocity for time reduction in plot [km/s]

degrees
¶
Distances are in [deg] instead of [km], velocities in [deg/s] instead of [km/s].

accuracy
=MAXIMUM_RELATIVE_RMS
¶ Set accuracy for model simplification.

slowness
=FLOAT
¶ Select surface slowness [s/km] (default: 0)

interface
=(NAME or DEPTH)
¶ Name or depth [km] of interface to select
Command line examples¶
Plot P and p phases¶
Ten receiver distances ranging from 100 km to 1000 km and a source depth of 10km.
cake plotrays crust2loc=45,10 phases=P,p sdepth=10 distances=100:1000:10
The option crust2loc
refers to the pyrocko.crust2x2
module and expects latitude and longitude of the source location.
Some water multiples¶
Receivers may be at any depth. Arbitrary reflection/conversion histories may be choosen.
cake plotrays sdepth=15 distances=10 rdepth=4.443 crust2loc=0,0 \
phase='pP\,pPv3pP\,pPv3pPv3pP\,p'
To print arrival times and other ray parameters, replace plotrays
with
arrivals
in the command line above.
> cake arrivals sdepth=15 distances=10 rdepth=4.443 crust2loc=0,0 \
phase='pP\,pPv3pP\,pPv3pPv3pP\,p'
slow dist time take inci effi spre phase used
s/km km s deg deg % %

0.09711 10.00 2.3147 128 10.6 58.7 103 p (p)
0.09099 10.00 8.1792 132 97.8 49.2 725 pP\ (p^0P\)
0.08461 10.00 14.052 136 97.3 8.03 729 pPv3pP\ (p^0Pv4.443p^0P\)
0.07835 10.00 19.931 140 96.8 1.32 710 pPv3pPv3pP\ (p^0Pv4.443p^0Pv4.443p^0P\)
Classic phase names¶
To use classic phase names, use the classic
option:
cake plotrays classic=Pdiff,PKP,PKIKP distances=110:150:5 degrees
Cake phases¶
It is possible to see the exact definition of a phase using cake print ...
:
> cake print classic=Pg
Phase definition "P<(moho)":
 P mode propagation, departing downward (may not propagate deeper than interface moho)
 arriving at target from below
Phase definition "p<(moho)":
 P mode propagation, departing upward (may not propagate deeper than interface moho)
 arriving at target from below
This tells us that the classic Pg phase is represented with two Cake style phase definitions, one for downgoing and one for upgoing takeoff direction and that there is a constraint on maximum depth.
Here’s another example to illustrate why cake needs its special phase definition syntax:
> cat >waveguide.nd <<EOF
0 4 2.3 2.6
1 3 1.73 2.6
2 4 2.3 2.6
EOF
> cake plotrays phases='P,p,P\,p\' sdepth=0.5 rdepth=1.5 distances=3,5 \
model=waveguide.nd
Material calculator¶
Cake can also be used to convert between different material parameters:
> cake print vp=5 poisson=0.25
P wave velocity [km/s] : 5
S wave velocity [km/s] : 2.88675
P/S wave vel. ratio : 1.73205
Lame lambda [GPa] : 21.6667
Lame shear modulus [GPa] : 21.6667
Poisson ratio : 0.25
Bulk modulus [GPa] : 36.1111
Young's modulus [GPa] : 54.1667
Rayleigh wave vel. [km/s] : 2.65408
Density [g/cm**3] : 2.6
Qp : 1350
Qs = Qmu : 600
Qk : inf
Energy scatter at interface¶
The scatter
subcommand may be used to see how much energy (in percent) is
transmitted through or reflected by an interface for any given surface
slowness (PSV case):
> cake scatter interface=moho slowness=0.0
interface "moho" (35 km)
4.349 3.209 95.65 96.79
\P /P \S /S /P /S
   
\P \S /P \P /S \S
95.65 96.79 4.349 3.209
> cake scatter interface=moho slowness=0.15
interface "moho" (35 km)
3.899 92.69 1.859 3.899 94.24 3.411
\P /S /P \S /S /P /S /P
  
\S \S /S \S
3.411 94.24 2.347
Python script examples¶
Calculate Pphase arrivals¶
The following Python script calculates arrival times for the Pphase emitted by an event in a depth of 300km.
'''
Calculate Pphase arrivals.
'''
from pyrocko import cake
import numpy as num
km = 1000.
# Load builtin 'premnoocean' model ('.m': medium resolution variant)
model = cake.load_model('premnoocean.m')
# Source depth [m].
source_depth = 300. * km
# Distances as a numpy array [deg].
distances = num.linspace(1500,3000,16)*km * cake.m2d
# Define the phase to use.
Phase = cake.PhaseDef('P')
# calculate distances and arrivals and print them:
print 'distance [km] time [s]'
for arrival in model.arrivals(distances, phases=Phase, zstart=source_depth):
print '%13g %13g' % (arrival.x*cake.d2m/km, arrival.t)