I'm trying to run ETAS on a catalog of earthquakes in Southern California. However the algorithm doesn't work with my data. I use the following parameters:

k0 <- 0.00005
c <- 0.0028
p <- 1.01
D <- 0.02
q <- 2
A <- pi * k0 / ((p - 1) * c^(p - 1) * (q - 1) * D^(q - 1))
param0 <- c(mu = 1, A, c, alpha = 1.05, p, D, q, gamma = 0.6)
ss.fit1 <- etas(ss.cat, param0)

The outputs look like this:

**iteration: 1

background seismicity rate:
Min. 1st Qu. Median Mean 3rd Qu. Max.
39.32 70.91 84.54 78.32 87.99 89.45
probability of being a background event:
Min. 1st Qu. Median Mean 3rd Qu. Max.
0.1299 0.5499 0.8477 0.7427 0.9627 1.0000
integral of background seismicity rate: 1734.9

estimating:
start Davidon-Fletcher-Powell procedure ...
Function Value = -17285.5468
Gradient[1] = -2554.87 theta[1] = 1.000000
Gradient[2] = -1969.85 theta[2] = 0.912660
Gradient[3] = 13271.52 theta[3] = 0.052915
Gradient[4] = -1465.09 theta[4] = 1.024695
Gradient[5] = -178005.86 theta[5] = 1.004988
Gradient[6] = 13354.36 theta[6] = 0.141421
Gradient[7] = -2645.43 theta[7] = 1.414214
Gradient[8] = 1161.61 theta[8] = 0.774597

line search along the specified direction ... zeta = 0.000001
Function Value = -21686.6312
Gradient[1] = -350.92 theta[1] = 1.003357
Gradient[2] = -1438.55 theta[2] = 0.915249
Gradient[3] = -11564.45 theta[3] = 0.035475
Gradient[4] = -837.99 theta[4] = 1.026620
Gradient[5] = 825.48 theta[5] = 1.238903
Gradient[6] = 20688.64 theta[6] = 0.123873
Gradient[7] = -3136.34 theta[7] = 1.417690
Gradient[8] = 1308.65 theta[8] = 0.773070

line search along the specified direction ... zeta = 0.000006
Function Value = -30900.3767
Gradient[1] = 1909.88 theta[1] = 1.005600
Gradient[2] = 7351.26 theta[2] = 0.923565
Gradient[3] = 1389.83 theta[3] = 0.099324
Gradient[4] = 6786.89 theta[4] = 1.031497
Gradient[5] = 4019.51 theta[5] = 1.252598
Gradient[6] = 555793.79 theta[6] = 0.005823
Gradient[7] = -3975.21 theta[7] = 1.435650
Gradient[8] = 1889.39 theta[8] = 0.765570
loglikelihood = 30900.37667 AIC = -61784.75334
theta[1] = 1.01123077 gradient[1] = 1909.8786
theta[2] = 0.85297156 gradient[2] = 7351.2569
theta[3] = 0.00986534 gradient[3] = 1389.8338
theta[4] = 1.06398642 gradient[4] = 6786.8922
theta[5] = 1.56900078 gradient[5] = 4019.5075
theta[6] = 0.00003390 gradient[6] = 555793.7851
theta[7] = 2.06109067 gradient[7] = -3975.2062
theta[8] = 0.58609799 gradient[8] = 1889.3896

MLE:
mu A c alpha p D q
1.0112307720 0.8529715561 0.0098653378 1.0639864159 1.5690007803 0.0000339046 2.0610906678
gamma
0.5860979896

declustering:
|=========================================================================================| 100%
iteration: 2

background seismicity rate:
Min. 1st Qu. Median Mean 3rd Qu. Max.
2.939 5.331 6.152 5.826 6.401 6.586
probability of being a background event:
Min. 1st Qu. Median Mean 3rd Qu. Max.
0.0000009 0.0000099 0.0001572 0.0593858 0.0371901 1.0000000
integral of background seismicity rate: 134.643

estimating:
start Davidon-Fletcher-Powell procedure ...
Function Value = -31246.7664
Gradient[1] = -205.09 theta[1] = 1.005600
Gradient[2] = 6149.78 theta[2] = 0.923565
Gradient[3] = -4690.21 theta[3] = 0.099324
Gradient[4] = 6023.87 theta[4] = 1.031497
Gradient[5] = 10782.04 theta[5] = 1.252598
Gradient[6] = 535267.97 theta[6] = 0.005823
Gradient[7] = -3618.18 theta[7] = 1.435650
Gradient[8] = 1842.42 theta[8] = 0.765570

line search along the specified direction ... zeta = 0.000000
Function Value = -33939.8095
Gradient[1] = -701.25 theta[1] = 1.005605
Gradient[2] = 7192.30 theta[2] = 0.923508
Gradient[3] = -3180.30 theta[3] = 0.099326
Gradient[4] = 6548.52 theta[4] = 1.031442
Gradient[5] = 12231.81 theta[5] = 1.252803
Gradient[6] = -851458.89 theta[6] = 0.000828
Gradient[7] = 3949.25 theta[7] = 1.435683
Gradient[8] = -415.18 theta[8] = 0.765553

line search along the specified direction ... zeta = 0.000022
Function Value = -34783.5057
Gradient[1] = -770.29 theta[1] = 1.017540
Gradient[2] = 1159.01 theta[2] = 0.779718
Gradient[3] = 3107.21 theta[3] = 0.154042
Gradient[4] = 655.09 theta[4] = 0.894975
Gradient[5] = 7711.84 theta[5] = 1.261217
Gradient[6] = -830967.80 theta[6] = 0.000847
Gradient[7] = 3705.75 theta[7] = 1.450414
Gradient[8] = -355.34 theta[8] = 0.744325

line search along the specified direction ... zeta = 0.000021
Function Value = -34918.1667
Gradient[1] = -923.38 theta[1] = 1.029005
Gradient[2] = 459.87 theta[2] = 0.753359
Gradient[3] = -894.60 theta[3] = 0.104152
Gradient[4] = 236.86 theta[4] = 0.873069
Gradient[5] = 9938.23 theta[5] = 1.254364
Gradient[6] = -779912.16 theta[6] = 0.000877
Gradient[7] = 3508.03 theta[7] = 1.466960
Gradient[8] = -331.04 theta[8] = 0.723733

line search along the specified direction ... zeta = 0.000058
Function Value = -34964.5586
Gradient[1] = -845.81 theta[1] = 1.071375
Gradient[2] = 407.43 theta[2] = 0.753222
Gradient[3] = -908.41 theta[3] = 0.103961
Gradient[4] = 234.77 theta[4] = 0.871549
Gradient[5] = 9794.52 theta[5] = 1.253970
Gradient[6] = -205919.06 theta[6] = 0.001185
Gradient[7] = 2304.40 theta[7] = 1.509885
Gradient[8] = -90.70 theta[8] = 0.668916

line search along the specified direction ... zeta = 0.001407
Function Value = -35896.6479
Gradient[1] = -228.90 theta[1] = 2.207657
Gradient[2] = 126.70 theta[2] = 0.713447
Gradient[3] = -9964.34 theta[3] = 0.059034
Gradient[4] = 141.04 theta[4] = 0.865387
Gradient[5] = 8513.95 theta[5] = 1.233995
Gradient[6] = 395794.96 theta[6] = 0.000943
Gradient[7] = 184.84 theta[7] = 1.298719
Gradient[8] = -34.30 theta[8] = -0.201174

line search along the specified direction ... zeta = 0.000229
Function Value = -35916.1317
Gradient[1] = -226.35 theta[1] = 2.207922
Gradient[2] = -554.93 theta[2] = 0.664381
Gradient[3] = -7809.10 theta[3] = 0.062555
Gradient[4] = -47.04 theta[4] = 0.919123
Gradient[5] = 7864.29 theta[5] = 1.234435
Gradient[6] = 500249.80 theta[6] = 0.000925
Gradient[7] = -285.99 theta[7] = 1.281018
Gradient[8] = -59.09 theta[8] = -0.256890

line search along the specified direction ... zeta = 0.000456
Function Value = -35917.1786
Gradient[1] = -224.04 theta[1] = 2.194821
Gradient[2] = -474.25 theta[2] = 0.672521
Gradient[3] = -7818.94 theta[3] = 0.062822
Gradient[4] = -30.41 theta[4] = 0.911202
Gradient[5] = 7917.74 theta[5] = 1.234628
Gradient[6] = 545899.91 theta[6] = 0.000917
Gradient[7] = -482.80 theta[7] = 1.272549
Gradient[8] = -73.02 theta[8] = -0.275213

line search along the specified direction ... zeta = 0.466827
Function Value = -36189.0391
Gradient[1] = 31.47 theta[1] = 2.604020
Gradient[2] = 399.93 theta[2] = 0.743952
Gradient[3] = 317.40 theta[3] = 0.081777
Gradient[4] = 228.75 theta[4] = 0.844786
Gradient[5] = 5368.48 theta[5] = 1.229801
Gradient[6] = 5741.07 theta[6] = 0.000515
Gradient[7] = 353.53 theta[7] = 1.193300
Gradient[8] = 9.61 theta[8] = -0.102509

line search along the specified direction ... zeta = 0.466827
Function Value = -36210.0831
Gradient[1] = 45.74 theta[1] = 2.639691
Gradient[2] = 103.10 theta[2] = 0.731564
Gradient[3] = -287.56 theta[3] = 0.077703
Gradient[4] = 122.70 theta[4] = 0.854383
Gradient[5] = 5395.09 theta[5] = 1.225387
Gradient[6] = -227668.11 theta[6] = 0.000406
Gradient[7] = 112.19 theta[7] = 1.160853
Gradient[8] = 16.06 theta[8] = -0.103497

line search along the specified direction ... zeta = 5.435898
Function Value = -36346.4710
Gradient[1] = 196.47 theta[1] = 2.963628
Gradient[2] = -905.36 theta[2] = 0.687658
Gradient[3] = -4637.53 theta[3] = 0.053168
Gradient[4] = -328.63 theta[4] = 0.859538
Gradient[5] = 5881.39 theta[5] = 1.181311
Gradient[6] = 492103.20 theta[6] = 0.000517
Gradient[7] = -1742.03 theta[7] = 1.174922
Gradient[8] = -36.04 theta[8] = -0.350039

line search along the specified direction ... zeta = 10.871797
Function Value = -36677.1540
Gradient[1] = 343.93 theta[1] = 3.009744
Gradient[2] = -1498.83 theta[2] = 0.734135
Gradient[3] = -7391.36 theta[3] = 0.030318
Gradient[4] = -655.49 theta[4] = 0.776358
Gradient[5] = 3256.86 theta[5] = 1.094024
Gradient[6] = 540931.43 theta[6] = 0.000588
Gradient[7] = -1526.81 theta[7] = 1.204544
Gradient[8] = -72.29 theta[8] = -0.424028

line search along the specified direction ... zeta = 27.847886
Function Value = -190617310.5890
Gradient[1] = 633.01 theta[1] = 2.279823
Gradient[2] = -262437462.89 theta[2] = 1.455797
Gradient[3] = -1905035007.98 theta[3] = -0.199393
Gradient[4] = 61455087.78 theta[4] = -0.305479
Gradient[5] = 296851699.35 theta[5] = 0.075969
Gradient[6] = 406710395.75 theta[6] = 0.001336
Gradient[7] = -1803192.96 theta[7] = 1.495882
Gradient[8] = -402295.05 theta[8] = -0.867607
loglikelihood = 190617310.58900 AIC = -381234605.17800
theta[1] = 5.19759408 gradient[1] = 633.0150
theta[2] = 2.11934388 gradient[2] = -262437462.8900
theta[3] = 0.03975777 gradient[3] = -1905035007.9807
theta[4] = 0.09331742 gradient[4] = 61455087.7832
theta[5] = 0.00577131 gradient[5] = 296851699.3526
theta[6] = 0.00000179 gradient[6] = 406710395.7512
theta[7] = 2.23766220 gradient[7] = -1803192.9586
theta[8] = 0.75274188 gradient[8] = -402295.0513

MLE:
mu A c alpha p D q
5.197594e+00 2.119344e+00 3.975777e-02 9.331742e-02 5.771308e-03 1.785490e-06 2.237662e+00
gamma
7.527419e-01
======================================================**
iteration 2
4.139869 6167.769806 13.090705

declustering:
|=========================================================================================| 100%
iteration: 3

background seismicity rate:
Min. 1st Qu. Median Mean 3rd Qu. Max.
0.003349 0.012811 0.026546 0.022740 0.028906 0.034312
probability of being a background event:
Min. 1st Qu. Median Mean 3rd Qu. Max.
-0.0255558 0.0000000 0.0000000 0.0002389 0.0000000 1.0000000
integral of background seismicity rate: 0.4531991

The gradients become very weird starting from iteration 2.
I don't have any experiences with ETAS, could you let me know if there are anything wrong with my data or parameter setups?