Fetch Live Earthquakes from USGS

-- fetch_earthquakes.lua — Live USGS earthquake data (last 30 days)
--
-- Fetches real-time earthquake data directly from the USGS API.
-- DuckDB's httpfs extension reads the CSV over HTTPS — no local download needed.
-- Scatter plot maps magnitude vs depth. City View works well with
-- height=mag, color=magType, district=place.

ds.log("=== USGS Earthquakes — Last 30 Days ===")
ds.log("Fetching live data from earthquake.usgs.gov...")

ds.query([[
    SELECT
        time,
        round(latitude, 3)  AS latitude,
        round(longitude, 3) AS longitude,
        round(depth, 1)     AS depth_km,
        round(mag, 1)       AS magnitude,
        magType              AS mag_type,
        nst                  AS station_count,
        round(gap, 0)::int  AS azimuthal_gap,
        round(dmin, 2)      AS distance_deg,
        round(rms, 3)       AS rms_residual,
        net                  AS network,
        place,
        type                 AS event_type,
        status,
        updated
    FROM read_csv_auto(
        'https://earthquake.usgs.gov/earthquakes/feed/v1.0/summary/all_month.csv'
    )
    WHERE mag IS NOT NULL
    ORDER BY time DESC
]])

ds.log("Loaded " .. ds.data.row_count .. " seismic events")
ds.log("Columns: " .. table.concat(ds.data.column_names, ", "))

-- Scatter: magnitude vs depth
ds.chart.type  = "scatter"
ds.chart.x     = 4       -- depth_km
ds.chart.y     = {5}     -- magnitude
ds.chart.title = "Earthquake Magnitude vs Depth (Last 30 Days)"

ds.log("=== Chart ready ===")
ds.log("Try: SELECT place, magnitude, depth_km FROM _cl_result WHERE magnitude > 4 ORDER BY magnitude DESC")