Earth Science — Seismic Wave Propagation

{
  "nodes": [
    {
      "id": "sw-focus",
      "type": "star",
      "label": "Focus (hypocentre) — where rupture begins, anywhere from 0 to 700 km deep",
      "x": 60,
      "y": 60,
      "width": 240,
      "height": 117,
      "fill": "#fee2e2",
      "stroke": "#b91c1c"
    },
    {
      "id": "sw-p",
      "type": "wave",
      "label": "P wave — compressional, particles move along the ray; 6 km s⁻¹ in crust, 13.7 km s⁻¹ in the deep mantle; crosses solids AND liquids",
      "x": 340,
      "y": 60,
      "width": 240,
      "height": 117,
      "fill": "#ede9fe",
      "stroke": "#6d28d9"
    },
    {
      "id": "sw-moduli",
      "type": "note",
      "label": "Speed follows from the elastic moduli and density: v_P = √((K + 4µ/3)/ρ) and v_S = √(µ/ρ). A liquid has rigidity µ = 0, so v_S = 0 — S waves simply stop.",
      "x": 620,
      "y": 410,
      "width": 240,
      "height": 117,
      "fill": "#fef9c3",
      "stroke": "#ca8a04"
    },
    {
      "id": "sw-crust",
      "type": "layers",
      "label": "Crust — 7 km under the oceans, 30–50 km under the continents",
      "x": 900,
      "y": 60,
      "width": 240,
      "height": 117,
      "fill": "#dbeafe",
      "stroke": "#1d4ed8"
    },
    {
      "id": "sw-outer",
      "type": "sphere",
      "label": "Outer core — 2891 to 5150 km: liquid Fe–Ni. No S waves; P speed drops from 13.7 to 8 km s⁻¹",
      "x": 1180,
      "y": 60,
      "width": 240,
      "height": 117,
      "fill": "#fee2e2",
      "stroke": "#b91c1c"
    },
    {
      "id": "sw-epi",
      "type": "location-pin",
      "label": "Epicentre — the surface point directly above the focus",
      "x": 60,
      "y": 235,
      "width": 240,
      "height": 117,
      "fill": "#fce7f3",
      "stroke": "#be185d"
    },
    {
      "id": "sw-s",
      "type": "wave",
      "label": "S wave — shear, particles move across the ray; ≈ 0.58 × the P speed; cannot pass through a liquid",
      "x": 340,
      "y": 235,
      "width": 240,
      "height": 117,
      "fill": "#ede9fe",
      "stroke": "#6d28d9"
    },
    {
      "id": "sw-moho",
      "type": "dimension-line",
      "label": "Mohorovičić discontinuity — the crust/mantle boundary, found in 1909 from a kink in P-wave travel times",
      "x": 900,
      "y": 235,
      "width": 240,
      "height": 117,
      "fill": "#fef3c7",
      "stroke": "#b45309"
    },
    {
      "id": "sw-inner",
      "type": "sphere",
      "label": "Inner core — 5150 to 6371 km: solid Fe–Ni, shown by PKiKP reflections and inner-core shear phases",
      "x": 1180,
      "y": 235,
      "width": 240,
      "height": 117,
      "fill": "#dbeafe",
      "stroke": "#1d4ed8"
    },
    {
      "id": "sw-station",
      "type": "gauge-chart",
      "label": "Seismograph station — records P first, then S, then the surface waves",
      "x": 60,
      "y": 410,
      "width": 240,
      "height": 117,
      "fill": "#fce7f3",
      "stroke": "#be185d"
    },
    {
      "id": "sw-love",
      "type": "wave",
      "label": "Love wave — horizontal shear confined to the surface; the faster of the two surface waves",
      "x": 340,
      "y": 410,
      "width": 240,
      "height": 117,
      "fill": "#ede9fe",
      "stroke": "#6d28d9"
    },
    {
      "id": "sw-mantle",
      "type": "layers",
      "label": "Mantle — down to 2891 km: solid, but convecting over geological time",
      "x": 900,
      "y": 410,
      "width": 240,
      "height": 117,
      "fill": "#dbeafe",
      "stroke": "#1d4ed8"
    },
    {
      "id": "sw-pshadow",
      "type": "rect",
      "label": "P shadow zone — 103° to 142° from the epicentre, produced by refraction at the core–mantle boundary",
      "x": 1180,
      "y": 410,
      "width": 240,
      "height": 117,
      "fill": "#fee2e2",
      "stroke": "#b91c1c"
    },
    {
      "id": "sw-sp",
      "type": "note",
      "label": "The S–P interval gives the distance — roughly 8 km for every second of lag. Three stations' distance circles intersect at the epicentre: that is triangulation.",
      "x": 60,
      "y": 585,
      "width": 240,
      "height": 117,
      "fill": "#fef9c3",
      "stroke": "#ca8a04"
    },
    {
      "id": "sw-rayleigh",
      "type": "wave",
      "label": "Rayleigh wave — retrograde elliptical rolling; slowest, largest amplitude, and the one that does the damage",
      "x": 340,
      "y": 585,
      "width": 240,
      "height": 117,
      "fill": "#ede9fe",
      "stroke": "#6d28d9"
    },
    {
      "id": "sw-cmb",
      "type": "dimension-line",
      "label": "Gutenberg discontinuity (core–mantle boundary) at 2891 km — P waves refract sharply, S waves stop dead",
      "x": 900,
      "y": 585,
      "width": 240,
      "height": 117,
      "fill": "#fef3c7",
      "stroke": "#b45309"
    },
    {
      "id": "sw-sshadow",
      "type": "rect",
      "label": "S shadow zone — everywhere beyond 103°. The cleanest single piece of evidence that the outer core is liquid",
      "x": 1180,
      "y": 585,
      "width": 240,
      "height": 117,
      "fill": "#fee2e2",
      "stroke": "#b91c1c"
    }
  ],
  "edges": [
    {
      "id": "sw-e1",
      "source": "sw-focus",
      "target": "sw-p",
      "label": "first to leave and first to arrive"
    },
    {
      "id": "sw-e2",
      "source": "sw-focus",
      "target": "sw-s"
    },
    {
      "id": "sw-e3",
      "source": "sw-focus",
      "target": "sw-epi",
      "label": "directly above"
    },
    {
      "id": "sw-e4",
      "source": "sw-epi",
      "target": "sw-love",
      "label": "surface waves radiate outward"
    },
    {
      "id": "sw-e5",
      "source": "sw-epi",
      "target": "sw-rayleigh"
    },
    {
      "id": "sw-e6",
      "source": "sw-p",
      "target": "sw-station",
      "label": "first arrival"
    },
    {
      "id": "sw-e7",
      "source": "sw-s",
      "target": "sw-station",
      "label": "second arrival"
    },
    {
      "id": "sw-e8",
      "source": "sw-love",
      "target": "sw-station"
    },
    {
      "id": "sw-e9",
      "source": "sw-rayleigh",
      "target": "sw-station",
      "label": "largest amplitude, arrives last"
    },
    {
      "id": "sw-e10",
      "source": "sw-crust",
      "target": "sw-moho"
    },
    {
      "id": "sw-e11",
      "source": "sw-moho",
      "target": "sw-mantle"
    },
    {
      "id": "sw-e12",
      "source": "sw-mantle",
      "target": "sw-cmb"
    },
    {
      "id": "sw-e13",
      "source": "sw-p",
      "target": "sw-moho",
      "label": "refracts, 1909",
      "style": "dotted",
      "arrowEnd": false
    },
    {
      "id": "sw-e14",
      "source": "sw-p",
      "target": "sw-mantle",
      "label": "speeds up 8 → 13.7 km s⁻¹",
      "style": "dotted",
      "arrowEnd": false
    },
    {
      "id": "sw-e15",
      "source": "sw-cmb",
      "target": "sw-outer",
      "label": "P refracts sharply, speed falls to 8 km s⁻¹"
    },
    {
      "id": "sw-e16",
      "source": "sw-outer",
      "target": "sw-inner",
      "label": "PKiKP reflects off the inner core"
    },
    {
      "id": "sw-e17",
      "source": "sw-outer",
      "target": "sw-pshadow",
      "label": "bending leaves 103°–142° unlit"
    },
    {
      "id": "sw-e18",
      "source": "sw-s",
      "target": "sw-cmb",
      "label": "absorbed here",
      "style": "dotted",
      "arrowEnd": false
    },
    {
      "id": "sw-e19",
      "source": "sw-cmb",
      "target": "sw-sshadow",
      "label": "nothing shear-like gets past"
    }
  ]
}