chore: initial Observable workspace with technical README

docs/data/ca-earthquakes-last365d.json.js

@@ -0,0 +1,47 @@
+const now = new Date();
+const start = new Date(now.getTime() - 365 * 24 * 60 * 60 * 1000);
+
+const params = new URLSearchParams({
+  format: "geojson",
+  starttime: start.toISOString(),
+  endtime: now.toISOString(),
+  minmagnitude: "2.5",
+  minlatitude: "32",
+  maxlatitude: "42.5",
+  minlongitude: "-125",
+  maxlongitude: "-114",
+  orderby: "time-asc",
+});
+
+const url = `https://earthquake.usgs.gov/fdsnws/event/1/query?${params}`;
+const response = await fetch(url);
+if (!response.ok) {
+  throw new Error(`USGS request failed: ${response.status}`);
+}
+
+const payload = await response.json();
+const features = Array.isArray(payload.features) ? payload.features : [];
+
+const quakes = features
+  .map((feature) => {
+    const [longitude, latitude] = feature.geometry?.coordinates ?? [];
+    const mag = Number(feature.properties?.mag);
+    if (
+      !Number.isFinite(latitude) ||
+      !Number.isFinite(longitude) ||
+      !Number.isFinite(mag)
+    ) {
+      return null;
+    }
+    return {
+      id: feature.id,
+      latitude,
+      longitude,
+      mag,
+      place: feature.properties?.place ?? "",
+      time: feature.properties?.time ?? null,
+    };
+  })
+  .filter(Boolean);
+
+process.stdout.write(JSON.stringify(quakes));