Ambient-noise cross-correlation on the Ridgecrest South array

An hour of ambient noise on 600 channels, correlated against a virtual source at channel 7000 in 60 s segments, whitened over 1-2 Hz and stacked. Lab 1 of the DAS workshop. Needs the noise extra.

Two 2.4 GB files from the AI4EPS dataset on HuggingFace, downloaded once to ~/.cache/dasio/.

import os
import urllib.request
from datetime import timedelta

import matplotlib.pyplot as plt
import numpy as np

from dasio import DASdb
from dasio.noise import common_shot_pairs, xcorr_dataset

BASE = 'https://huggingface.co/datasets/AI4EPS/quakeflow_das/resolve/main/ridgecrest_south/data'
FILES = (
    'RidgeCrest-South-2026-01-02T133503Z.h5',
    'RidgeCrest-South-2026-01-02T140503Z.h5',
)
CACHE = os.path.expanduser('~/.cache/dasio')
CH0, CH1, SRC = 6700, 7300, 7000            # receiver range, virtual source

os.makedirs(CACHE, exist_ok=True)
for name in FILES:
    path = os.path.join(CACHE, name)
    if not os.path.exists(path):
        urllib.request.urlretrieve(f'{BASE}/{name}', path)

Catalog the cache. The two files are one contiguous hour: the first segment.

db = DASdb.from_dir(CACHE)
seg = next(db.segments())
begin = seg['begin_time'].iloc[0].to_pydatetime()
end = seg['end_time'].iloc[-1].to_pydatetime() + timedelta(seconds=1 / seg['fs'].iloc[0])

scan:   0%|          | 0/3 [00:00<?, ?file/s]
scan: 100%|██████████| 3/3 [00:00<00:00, 1757.39file/s]

ch1, ch2 = common_shot_pairs(SRC - CH0, CH1 - CH0)   # indices into [CH0, CH1)
ccg = xcorr_dataset(
    db, ch1, ch2, begin=begin, end=end, min_ch=CH0, max_ch=CH1,
    seg_sec=60.0, max_lag_sec=4.0, window_sec=1800.0,
    prep=dict(
        freqmin=0.5, freqmax=10.0, norm_window_sec=0,
        differentiate=True, detrend=False, subtract_common_mode=True,
    ),
    whiten=True, whiten_band=(1.0, 2.0),
)

ax, im = ccg.plot(offsets=np.arange(CH0, CH1), perc=98, figsize=(10, 8))
ax.axvline(SRC, color='k', ls='--', lw=1, label='virtual source')
ax.set_xlabel('channel')
ax.legend(loc='upper right')
ax.set_title('Virtual-shot gather at channel 7000, ambient noise, 0.5-10 Hz')
plt.show()